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S1 Fig: Gating strategy for peripheral blood ILC1 subsets. (A) Representative dot plots identify ILC1 subsets.
After gating on lymphocytes (FSC-SSC), singlets, and live CD45 + cells, the cells that remained were identified as lineage -CD127 -CD56 + NK cells and lineage -CD127 +CD56 - total ILC1 cells. Based on CD4 and CD8 expression, ILC1s were further divided into CD4 +CD8 -, CD4 -CD8 + and CD4 -CD8 - ILC1s, while the NK cells did not contain any CD4 +CD8 - cell subpopulations. The lineage markers included CD3, CD14, CD16, CD19, CD123, CD11c, CD34, CD117 (excluding ILC3) and CD294 (CRTH2, excluding ILC2). The numbers indicate the percentage of cell subsets.
(B) A representative histogram shows the expression of TCRαβ, TCRγδ, CD5 and CD94 expression on various ILC1 subsets and NK cells. Shade, isotype control; black curve, markers above. S5 Fig: Activation enhances HIV-1 infection in T cells. ( A) Representative dot plots indicate p24 expression within CD3 + T cells present in vitro of mock or HIV-1 NL4-3 stock with or without activation (PHA pre-stimulation for 24 hours). ( B) Summarized data indicate the percentages of p24 + cells within CD3 + T cells in various conditions. Human PBMCs were first incubated with PHA for 24 hours in the presence of IL-2 (50 IU/ml) and IL-7 (20 ng/ml). The cells were then incubated with HIV/NL4-3 stock or mock stock for additional 4 days.
S8 Fig: Absence of any effect of HIV-1 infection on the expression of caspase 1 and DR5 by ILC1 subsets. ( A) The representative dot plots depict the expression of caspase 1 on CD4 + and CD4 - ILC1 subsets in the peripheral blood of various groups.
The numbers indicate the percentages of cell subsets. ( B) Summary data of caspase 1 expression in peripheral blood CD4 + and CD4 - ILC1s in the HC (n = 15), HIV-1 (n = 27) and HIV-1 plus HAART groups (n = 5). ( C) Representative dot plots depict DR5 expression on CD4 + and CD4 - ILC1 subsets in the peripheral blood of various human patients. The numbers indicate percentages of gated cell subsets. ( D) Summary data of DR5 expression in peripheral blood CD4 + and CD4 - ILC1s in the HC (n = 6), HIV-1 (n = 6) and HIV-1 plus HAART groups (n = 5). ( B and D) Data represent the mean ± s.e.m. S10 Fig: The function of ILC-1 in humanized mice with cART and IFNAR blockade.
Humanized mice infected with HIV-1 were treated with cART from 4–12 weeks post infection (wpi). From 7 to 10 wpi, the cART-treated mice were injected with α-IFNAR1 antibody or isotype control mIgG2a antibody twice a week. Mice were terminated at 12wpi. (A) Representative dot plots show the production of IFN-γ and TNF-α by splenic ILC1s from various groups of humanized mice after stimulation with PMA/ionomycin (n = 5 for each group).
Numbers indicate the percentages of cytokine-expressing cell subsets. ( B) Summarized data of IFN-γ and TNF-α production in response to PMA/ionomycin of splenic ILC1s from mock, HIV-1-infected mice, HIV-1-infected mice with cART plus mIgG2a isotype antibody or α-IFNAR mAb. Data represent the mean ± s.e.m.
Innate lymphoid cells (ILCs) are severely depleted during chronic HIV-1 infection by unclear mechanisms. We report here that human ILC1s comprising of CD4 + and CD4 - subpopulations were present in various human lymphoid organs but with different transcription programs and functions. Importantly, CD4 + ILC1s expressed HIV-1 co-receptors and were productively infected by HIV-1 in vitro and in vivo. Furthermore, chronic HIV-1 infection activated and depleted both CD4 + and CD4 - ILC1s, and impaired their cytokine production activity. Highly active antiretroviral (HAART) therapy in HIV-1 patients efficiently rescued the ILC1 numbers and reduced their activation, but failed to restore their functionality.
We also found that blocking type-I interferon (IFN-I) signaling during HIV-1 infection in vivo in humanized mice prevented HIV-1 induced depletion or apoptosis of ILC1 cells. Therefore, we have identified the CD4 + ILC1 cells as a new target population for HIV-1 infection, and revealed that IFN-I contributes to the depletion of ILC1s during HIV-1 infection. Innate lymphoid cells (ILCs), including ILC1, ILC2 and ILC3 populations, represent a novel cellular family of the immune system and have potentials to produce large amounts of T cell-associated cytokines in response to innate stimulation in the absence of specific antigen stimulation. ILCs have emerged as central players in homeostatic and inflammatory conditions, and correlated with the pathogenesis and progression of multiple human diseases. It is reported that ILCs are depleted in HIV-1 infected patients. However, it is not clear whether HIV-1 can infect ILCs and how ILCs are depleted during HIV-1 infection.
Here, we find that ILC1s consist CD4 + and CD4 - subsets and both are present in various human lymphoid organs. We show that HIV-1 can directly infect CD4 + ILC1s. HIV-1 infection leads to activation, depletion and functional impairment of ILC1s in humans and in humanized mice in vivo. Blocking IFN-I signaling prevents HIV-1-induced apoptosis of ILC1s both in vitro and in humanized mice in vivo. Our study reveals the CD4 + ILC1 population as a new target for HIV-1 infection and identifies an IFN-I mediated mechanism of ILC1 depletion during chronic HIV-1 infection.
Presence of CD4 +, CD8 + and CD4 -CD8 - ILC1 subsets in various human lymphoid organs and their transcription, phenotypes and functionality It was recently reported that ILC1s in human peripheral blood contain CD4 +, CD8 + and CD4 -CD8 - subpopulations ; however, it is unclear whether these cell populations are present in human lymphoid organs. Here, we investigated the distribution of each ILC1 subpopulation in various human lymph organs.
By gating on live human CD45 + cells that were negative for lineage-specific surface markers of B cells (CD19 and CD20), T cells (CD3), conventional natural killer (NK) cells (CD16), monocytes and dendritic cells (CD14, CD11c and CD123), and surface markers of hematopoietic precursors (CD34), ILC2 cells (CRTH2) as well as ILC3 cells (CD117), we identified ILC1s as hCD45 +Lin -CD117 -CRTH2 -CD127 +CD56 - cells. Similar to the results of a previous study , we found that ILC1s comprise of CD4 +CD8 -, CD4 -CD8 + and CD4 -CD8 - subpopulations. All the ILC1 subsets don’t express the T cell marker TCRαβ, TCRγδ and NK cell marker CD94 which excludes T cell and NK cell contamination; while they express CD5.
More importantly, we found that the all the three ILC1 subsets, including CD4 + ILC1s, were all present in various human lymphoid organs including the spleen, bone marrow, large intestine, small intestine and liver perfusion. Further analysis indicated that CD45 + cells constituted 0.019%–0.818% of the total ILC1 cells and CD4 + ILC1s constituted 2.35%–39.2% of the total ILC1s in different organs. Identification of the CD4 +, CD8 + and CD4 -CD8 - ILC1 subsets in human lymphoid organs. ( A) The representative dot plots show the tissue distribution of CD4 +, CD8 +, and CD4 -CD8 - ILC1 subsets in the peripheral blood, spleen, bone marrow, large intestine, small intestine and liver perfusion. The numbers indicate the percentages of each cell subset. ( B-C) Summary data of the proportion of total ILC1s in live CD45 + cells ( B) and the proportion of CD4 + ILC1s in the total ILC1s ( C) in various lymphoid organs in humans (n = 25 for PBMCs and n = 5 for other organs). ( D) Representative dot plots depict the expression of transcriptional factor T-bet and Eomes of CD4 +, CD8 + and CD4 -CD8 - ILC1 subsets in peripheral blood of human.
The numbers indicate the percentages of transcriptional factors within each ILC1 subset. ( E) Summary data of the expression of T-bet and Eomes by ILC1 subsets in peripheral blood of human (n = 15). ( F-G) Summarized data show the production of IFN-γ and TNF-α by peripheral ILC1 subsets from healthy subjects after stimulation with PMA/ionomycin (n = 12, F) and IL-12 plus IL-18 (n = 12, G). ( B, C, E-G) Data represent the mean ± s.e.m. In vitro and in vivo infection of CD4 + ILC1s by HIV-1 Since a significant proportion of ILC1s express CD4, the receptor for HIV-1 infection, we investigated whether HIV-1 can infect CD4 + ILC1s.
First, we examined the expression of the HIV-1 co-receptors CCR5 and CXCR4 on ILC1s by flow cytometry. Both CCR5 and CXCR4 were expressed on CD4 + ILC1s from human PBMCs and the spleen of humanized mice. CD4 - ILC1s also expressed comparable levels of CCR5 and CXCR4. Further analyses indicated that 12% of human CD4 + ILC1s express CCR5, while 60% express CXCR4. The expression of CCR5 and CXCR4 was also detected on CD4 + ILC1s in lymphoid organs, including the spleen, peripheral lymph node and bone marrow, and peripheral blood from humanized mice, but the expression level was slightly lower than that in human PBMCs.
HIV-1 infects ILC1 cells. ( A) Representative histograms indicate the expression of the HIV-1 co-receptors CCR5 and CXCR4 on CD4 + and CD4 - ILC1s from the spleen of humanized mouse and human peripheral blood. ( B) Summary data show the expression of CCR5 and CXCR4 by CD4 + ILC1s from human PBMCs (n = 6) and the spleen (n = 14), BM (n = 4), mLN (n = 4) and PBL (n = 3) of humanized mice.
BM, bone marrow; mLN, mesenteric lymph node; pLN, popliteal lymph node. ( C-D) Representative dot plots ( C) and summarized data ( D) indicate the p24 + ILC1s present in vitro of HIV-1 stock. The numbers ( C) indicate the percentages of p24 + cells within ILC1s. Human fresh PBMCs were infected with HIV-1 (R3A and NL4-3) in vitro without or with anti-HIV-1 neutralizing antibody.
Increased activation and proliferation of CD4 + and CD4 - ILC1s in patients with chronic HIV-1 infection We next investigated whether HIV-1 infection also activates ILC1s in patients. We analyzed the expression of CD38 and Ki-67 in ILC1s ( and ). Both CD4 + and CD4 - ILC1s expressed higher levels of CD38 and Ki67 in HIV-1-infected patients than in the healthy control (HC) subjects, while highly active antiretroviral therapy (HAART) reduced the activation and proliferation of both CD4 + and CD4 - ILC1s. As expected, HIV-1 also activated CD8 T cells in HIV-infected patients, and that the activation level was significantly decreased after HAART.
Further, the percentage of Ki67-expressing CD4 + ILC1s, but not CD4 - ILC1s, was found to positively correlate with the plasma HIV-1 viral load. In contrast, Ki-67 expression in CD8 T cells was not correlated with plasma HIV-1 load in these patients. These data indicate that HIV-1 infection activated both CD4 + and CD4 - ILC1s. In particular, the activation of CD4 + ILC1s, the HIV-1 target population, was positively correlated with the HIV-1 viral load.
Activation of ILC1s during chronic HIV-1 infection. ( A- B) Representative dot plots ( A) and summarized data ( B) show the expression of the activation marker CD38 and proliferation marker Ki67 on CD4 + and CD4 - ILC1 subsets from the peripheral blood of the healthy donor (n = 18), HIV-1 (n = 30) and HIV-1 plus HAART groups (n = 7). The numbers ( A) indicate the percentages of each cell subset. ( C- D) Representative dot plots ( C) and summarized data ( D) show the expression of the activation marker CD38 and the proliferation marker Ki67 on CD8 T cells from the peripheral blood of the healthy donor (n = 15), HIV-1 (n = 18) and HIV-1 plus HAART groups (n = 7). The numbers ( C) indicate the percentages of each cell subset. Data represent the mean ± s.e.m. Preferential depletion of CD4 + ILC1s during chronic HIV-1 infection and its correlation with the progression of HIV-1 infection We next investigated whether HIV-1 infection depletes ILC1s in vivo.
Compared to the HCs, ILC1s in CD45 + cells were significantly reduced in the peripheral blood of patients with chronic HIV-1 infection , and HAART partially reversed the reduction of total ILC1s. Further analysis indicated that the percentage of both CD4 + and CD4 - ILC1s in total CD45 + cells was lower in patients with HIV-1 infection than in the HC subjects, while only the CD4 + ILC1s but not CD4 - ILC1s were significantly rescued by HAART. The absolute cell counts of total ILC1s and CD4 + and CD4 - ILC1s were found to be largely reduced in patients with chronic HIV-1 infection as compared to those of HC subjects; and HAART successfully recovered the absolute cell counts of total ILC1s and CD4 + ILC1s but not CD4 - ILC1s. Correlation analysis indicated that the percentage of peripheral CD4 + ILC1s was negatively correlated with the plasma HIV-1 viral load and positively correlated with the CD4/CD8 ratio in the HIV-1-infected subjects. Preferential depletion of CD4 + ILC1s during chronic HIV-1 infection and its correlation with disease progression. ( A) Representative dot plots show the proportion of ILC1 subsets within live CD45 +lineage - cells in the peripheral blood samples of the HC (n = 26), HIV-1 (n = 30) and HIV-1 plus HAART (n = 12) groups. The numbers indicate the percentages of cell subsets.
( B) Summarized data show the percentage of ILC1s in CD45 + cells. ( C) Summary data show the percentage of CD4 + and CD4 - ILC1 subsets in CD45 + cells or in total ILC1s in various groups. ( D) Summary data show the absolute cell counts of total ILC1s, and CD4 + and CD4 - ILC1 subsets in peripheral blood of various groups. ( E) Correlation analysis between the CD4 + ILC1 percentage in CD45 + cells and plasma HIV-1 load. The Spearman rank correlation test is used: r, correlation coefficient; p values are shown. ( F) Representative dot plots show the percentage of CD4 + ILC1s in the large intestine of a healthy donor and an HIV-1-inected patient. The numbers indicate the percentages of each cell subset.
( G– I) Summarized data show the percentage of ILC1s in CD45 + cells ( G) and the percentage of CD4 + or CD4 - ILC1 subsets in CD45 + cells ( H) or the total ILC1s ( I) from the large intestine in HCs (n = 5) and HIV-1-infected patients (n = 4). ( B-D, G–I) Data represent the mean ± s.e.m. Reduced capacity of ILC1 subsets to produce cytokines as a result of persistent HIV-1 infection in vivo ILC1s can produce large amounts of Th1-associated cytokines in response to innate stimulation. We next analyzed whether persistent HIV-1 infection affected the cytokine production ability of ILC1s. As shown in, IFN-γ and TNF-α production by both CD4 + and CD4 - ILC1 subsets induced by PMA/ionomycin stimulation were significantly lower in HIV-1-infected patients than in HCs.
Similar phenomena were also observed when the ILC1s were stimulated by IL-12 and IL-18. HAART failed to rescue the function of ILC1 subsets, with the exception that IFN-γ production was rescued by HAART after IL-12 and IL-18 stimulation.
We thus conclude that chronic HIV-1 infection impaired the ability of the remaining ILC1s, including CD4 + ILC1s, to produce cytokines. Induction of apoptosis of ILC1s in response to HIV-1 infection We next examined how HIV-1 infection leads to ILC1 depletion. We discovered that chronic HIV-1 infection significantly up-regulated active caspase-3 expression in both CD4 + and CD4 - ILC1s.
In contrast, caspase1 was not significantly up-regulated in CD4 + ILC1s (and only slightly increased in CD4 - ILC1s) of patients with HIV-1 infection as compared to the HC subjects. HAART could significantly decrease the expression of active caspase-3 in both CD4 + and CD4 - ILC1s , correlated with rescued ILC1s.
These findings indicate that HIV-1 infection leads to depletion of ILC1 subsets via apoptosis-dependent mechanisms. HIV-1 infection leads to ILC1 apoptosis. Representative dot plots ( A and C) and summary data ( B and D) show the percentage of active caspase-3-expressing and CD95-expressing CD4 + and CD4 - ILC1s in HCs (n = 15), HIV-1-infected patients without HAART (n = 21) and patients with HAART (n = 7).
The numbers indicate the percentages of cell subsets ( A and C). Role of IFN-I signaling in HIV-1 induced ILC1 depletion Sustained IFN-I signaling has been reported to be correlated with and contribute to SIV and HIV-1-induced immune pathogenesis –.
We have proved that depletion of pDCs or blocking IFN-I signaling prevents HIV-1-induced T cell and ILC3 depletion in vivo ,. We thus investigated whether IFN-I signaling also contributes to HIV-1-induced ILC1 depletion in vivo. We treated HIV-1-infected humanized mice with the anti-IFNAR1 mAb from week 6 through week 10 after infection. At 10–12 weeks after infection, we terminated the mice and measured ILC1 number and phenotype in each group. We found that blockade of IFN-I signaling with the anti-IFNAR1 mAb rescued both CD4 + and CD4 - ILC1s cells in percentages and in numbers as compared to the isotype IgG control group. In addition, we found that blocking the IFN-I pathway significantly decreased CD95 expression on CD4 + ILC1s in humanized mice with persistent HIV-1 infection. We further cultured PBMCs from HIV-1-infected patient ex vivo in the absence or presence of pDC-depleting 15B mAbs conjugated with the SAP toxin (immune toxin 15B-sap) or the anti-IFNα/β receptor blocking antibody.
We observed significant downregulation of both CD95 and active caspase-3 expression in CD4 + ILC1s from HIV-1-infected patients cultured in vitro in the presence of the immune toxin 15B-sap or anti-IFN-α/β receptor antibodies as compared to the IgG control. Therefore, depletion of pDCs or blockade of IFNAR1 both prevents HIV-1 induced ILC-1 depletion in vitro. These data indicate that IFN-I signaling contributes to ILC1 depletion during chronic HIV-1 infection. Prevention of ILC1 depletion by blockade of IFN-I signaling. ( A– D) Humanized mice infected with HIV-1 were treated with α-IFNAR mAb or isotype control (mouse IgG2a) twice a week from 6 to 10 weeks after infection.
Mice were sacrificed at 10 weeks after infection. ( A) Summary data show the percentage of ILC1s in the total CD45 + cells present in the spleen of humanized mice. ( B-C) Summary data show the percentage of CD4 + and CD4 - ILC1s in total CD45 + cells ( B) and in ILC1s ( C) present in the spleen of humanized mice, respectively. ( D) Absolute number of CD4 + and CD4 - ILC1s in the spleen of humanized mice. ( E-F) Representative dot plot ( E) and summarized data ( F) show CD95 expression on ILC1s in the spleen of humanized mice. ( A–D, F) Mock, n = 3; HIV-1 plus mIgG2a, n = 5; HIV-1 plus α-IFNAR, n = 5. Data are representative of three independent experiments with three donors.
Data represent the mean ± s.e.m. Discussion Our study investigates the heterogeneity of ILC1s in human lymphoid organs, and provides the first piece of evidence to show that HIV-1 can directly infect CD4 + ILC1s and lead to their activation, depletion and functional impairment in vivo in humans and in humanized mice. Successful HAART rescued the number of CD4 + ILC1s but not cytokine production activity via the inhibition of Fas/FasL-mediated apoptosis of ILC1s. This study, therefore, is the first to identify CD4 + ILC1s as important HIV-1 target cells, and may serve as a novel target of HIV-1 therapies aimed at human immune reconstitution. Through a comprehensive analysis of lymphocytes from human spleen, bone marrow, large intestine, small intestine and liver, we found that human ILC1s consist of CD4 +, CD8 + and CD4 -CD8 - populations and that all these populations are widely present in all lymphoid organs, which has not been described in previous studies ,.
We also observed that CD4 + ILC1s expressed immature phenotypes and lower levels of Th1-associated transcriptional factor T-bet and Eomes than CD4 - ILC1s and higher level of TNF-α in response to stimulation. It Is not clear where these CD4+ ILC1s are developed and how the immature ILC1 subsets traffic to various lymphoid tissues. A recent study based on mass cytometry- and t-SNE-based analysis showed ILC1s were undetectable across different human tissues. However, in a re-analysis on CyTOF dataset, ILC1s are clearly clustered in lymphoid tissues. Another report also suggested that ILC1s reported in previous studies may be attributable to CD5 + T cell contamination.
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However, CD5 is also expressed and functions independently of T cells. Indeed, ILC1s express high levels of CD5 in our study and previous report. Therefore, the use of CD5 with CD4 or CD8 in ILCs without confirming surface CD3 or TCR expression does not definitively identify CD4 + and CD8 + T cells. Furthermore, human patients with RAG1 deficiency, who lack T cells, are characterized by the presence of circulating ILC1s at frequencies comparable to those of ILC2s and ILC3s. ILC1s have also been cloned under T-cell-promoting conditions, and have been detected in inflamed intestinal tissues of patients suffering from Crohn’s diseases ,.
Taken together, our data provide a comprehensive description of the heterogeneity of CD4 + and CD4 - ILC1s (not T cells) across various lymphoid tissues in humans. The identification of CD4 expression on ILC1s led to the question of whether this population can be infected by HIV-1. Our results clearly showed that CD4 + ILC1s also express CCR5 and CXCR4 and can be productively infected by HIV-1 both in vitro and in vivo.
The relative infection and replication of HIV-1 in CD4 + ILC1s is comparable to that in CD4 T cells. Interestingly, PHA activation of PBMC enhanced HIV infection in both CD4+ ILC1 and T cells. These results indicate that CD4 + ILC1s are HIV-1 target cells and possibly support HIV-1 persistence in patients with chronic HIV-1 infection. Therefore, we identified CD4 + ILC1s as a new target for HIV-1 infection. Further studies to identify whether CD4 + ILC1s serve as an HIV-1 reservoir in HIV patients during HAART will be important for developing strategies for HIV-1 treatment. It has been reported that HIV-1 infection leads to depletion of all ILC subsets, including ILC1s, in circulation and lymphoid organs. We discovered here that HIV-1 infection also depleted ILC1s in the large intestine of patients.
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Unlike the results of a previous study , we found that HAART can rescue the number of peripheral ILC1s in HIV-1-infected patients. This discrepancy could be explained by the difference in the cohorts enrolled in the two studies. Differences in the time of HAART onset may lead to differences in immune reconstitution , , which may then affect the restoration of the number of ILC1s.
Our results indicate that HIV-1 infection depletes ILC1s both in circulation and in lymphoid organs. Of particular note, we found that CD4 + ILC1s were preferentially depleted within the total ILC1 population, which indicates that they are more sensitive to HIV-1-induced apoptosis. The mechanism underlying HIV-1-induced depletion of ILC1s is poorly defined. We have reported previously that HIV-1 infection induces depletion of ILC3s via Fas/FasL signaling in a pDC/IFN-I-dependent manner.
In the present study, we found that the depletion of ILC1s was also associated with cell apoptosis mediated by the Fas/FasL pathway during HIV-1 infection. We therefore tested the pDC/IFN-I axis in humanized mice with HIV-1 infection. Our data clearly showed that blocking IFN-I signaling with an antibody against IFNAR1 prevented HIV-1-induced depletion of ILC1s in vivo in humanized mice. Furthermore, blocking IFN-I signaling or depletion of pDCs during in vitro culture of PBMCs from HIV-1 infected patients also significantly reduced ILC1 apoptosis and rescued their number.
We thus have demonstrated that pDC and IFN-I signaling plays a critical role in ILC1 depletion during chronic HIV-1 infection. Our data demonstrate that HIV-1 infection not only depletes ILC1s but also leads to their activation and functional impairment, as indicated by the significant decrease observed in their production of cytokines, including IFN-γ and TNF-α. Interestingly, HAART rescues ILC1s in number but fails to recover their function of cytokine production in HIV-1-infected patients. In HIV-1-infected humanized mice, however, we found that HAART starting during early phase of infection (4wpi) rescued both ILC1 number and functions in IFN-γ and TNF-α production. This differential effect of HAART on ILC1 function may be due to different treatment time in patients and in humanized mice.
For patients in the study, HAART was usually initialized years after HIV-1 infection at chronic infection phase; while HAART was given at early phase of HIV-1 infection (4 weeks) for humanized mice in the study. Indeed, our findings are similar to a previous report in which antiretroviral therapy initialized during acute infection could preserve ILCs in patients. These data also indicate that depletion of ILC1s and their functional impairment may be mediated by various mechanisms during short acute and long chronic infection. We have recently found that pDC depletion or blockade of IFN-I signaling could significantly reduce residual immune activation and restore anti-HIV immunity in HIV-1-infected humanized mice without or with cART. Future studies should focus on the differential mechanisms underlying cell depletion and functional impairment of ILC1 subsets, and determine whether HAART combined with IFN-I blockade can restore ILC1 function in chronic HIV-1 infection in human patients. In summary, we identified subset- and tissue-dependent heterogeneity of ILC1s and provided evidence to show that CD4 + ILC1s are a novel target for HIV-1 infection. Further, we demonstrated that IFN-I signaling contributes to the depletion of ILC1s, at least partly through the Fas/FasL pathway during HIV-1 infection.
These new findings, therefore, extend our earlier findings which show that sustained pDC activation and IFN-I production contributes to HIV-1 pathogenesis. Therefore, blockade of the pDC/IFN-I axis will be a novel therapeutic stratagem to reverse HIV-1-induced pathogenesis, including ILC1 depletion and impairment. Ethics statement Approval for animal work was obtained from the University of North Carolina Institutional Animal Care and Use Committee (IACUC ID: 14–100). The study protocol on human samples was approved by the Institutional Review Board and the Ethics Committee of Beijing 302 Hospital in China. The written informed consent was obtained from each subject. All samples were anonymized in the study. Human tissue samples, including the spleen, small intestine, large intestine, bone marrow and liver perfusion, used in this study were obtained from adult donors who had undergone liver transplantation as healthy controls.
Gut mucosa from HIV-1-infected patients were obtained for pathological diagnosis. Written informed consent was obtained from each donor.
Complete RPMI media were used for all cell isolation experiments. Human fetal livers and thymuses (gestational age 16 to 20 weeks) were obtained from medically indicated or elective termination of pregnancies through a non-profit intermediary working with outpatient clinics (Advanced Bioscience Resources, Alameda, CA). Written informed consent from the maternal donor was obtained in all cases under regulations governing the clinic. All animal studies were conducted following NIH guidelines for housing and care of laboratory animals. The project was reviewed by the University’s Office of Human Research Ethics, which determined that this submission does not constitute human subjects research as defined under federal regulations 45 CFR 46.102 (d or f) and 21 CFR 56.102(c)(e)(l).
Human tissue cell isolation Immune cells from human samples were isolated according to previously reported protocols. In brief, peripheral blood mononuclear cells (PBMCs) and bone marrow cells were isolated by Ficoll-Hypaque density gradient centrifugation of heparinized blood of enrolled subjects. The spleen was first ground on ice, after which the cells were collected and filtered.
The liver perfusion was directly filtered and concentrated by centrifugation (750 g, 15 min, 20°C), and was layered onto the Ficoll gradient. The small intestine and large intestine were first finely minced using scalpels, and were then incubated with 0.8 mg/mL collagenase type IV (Worthington-Biochemical) and DNase I (Roche) for 1 h before they were filtered through a 70-mm strainer.
The filtered cells were collected and isolated in a similar manner to PBMCs. Upon isolation, all the cells were cryopreserved in 90% fetal calf serum plus 10% DMSO for subsequent assay.
Construction of humanized mice We constructed NRG-hu mice using a previously reported method. Briefly, human CD34 + cells were isolated from 16- to 20-week-old fetal liver tissues (Advanced Bioscience Resources, Alameda, CA). The tissues were digested with liver digest medium (Invitrogen, Frederick, MD). The suspension was filtered through a 70-μm cell strainer (BD Falcon, Lincoln Park, NJ) and centrifuged for 5 min to isolate mononuclear cells by Ficoll gradient centrifugation.
After selection with the CD34 + magnetic-activated cell sorting (MACS) kit, CD34 + hematopoietic stem cells were injected into the liver of each irradiated (300 rad) 2- to 6-day-old NRG mouse (0.5 × 10 6/mouse). More than 95% of the humanized mice were stably reconstituted with human leukocytes in the blood (60%–90% at 12–14 weeks). The level of engraftment was similar in each cohort. All the mice were housed at the University of North Carolina at Chapel Hill. HIV-1 virus stocks and infection of humanized mice An R5-tropic strain of HIV-1, JR-CSF (NIH AIDS reagents program, Cat# 2708), was used for inducing persistent HIV-1 infection. Viruses were generated by transfection of 293T cells (SIGMA-ALORICH, Cat# 12022001-1VL).
R3A-HSA was constructed by replacing the vpr gene with mouse heat stable antigen (HSA; CD24) as reported previously. Humanized mice with stable human leukocyte reconstitution were infected with JR-CSF or R3A-HSA at a dose of 10 ng p24/mouse, through an intra-orbital injection. Humanized mice infected with mock-transfected 293T cell culture supernatant were used as control groups.
For acute HIV-1 infection, viral genomic RNA present in the plasma was measured by real-time PCR (ABI Applied Biosystem). An X4 and R5 dual-tropic strain of HIV-1, R3B/Av1v2, was used for the in vitro experiment. In vitro HIV-1 infection Fresh PBMCs were incubated with the infectious HIV-R3A stock, NL4-3 stock or mock stock with or without the neutralizing monoclonal antibody (Clone CH31) for 2 h at 37°C.
Then, the cells were incubated in complete RPMI 1640 medium at a density of 2 × 10 6 cells/ml in the presence of IL-2 (50 IU/ml) and IL-7 (20ng/ml) for an additional 3 days. Alternatively, fresh PBMCs were activated with phytohemagglutinin (PHA, 5 μg/ml) or medium in the presence of IL-2 (50 IU/ml) and IL-7 (20 ng/ml) for 24 hours. Then the cells were incubated with the infectious NL4-3 stock or mock stock for an additional 4 days. Intracellular p24 expression on ILC1 subsets or CD3 + T cells was determined by flow cytometry as described above. Blockade of human IFN-I signaling in NRG-humanized mice An anti-IFNAR1 blocking antibody was developed as per our recent report. Briefly, the human IFNAR1 expression cell line 293T was first incubated with the supernatant of the hybridoma and then incubated with the PE-labeled goat anti-mouse IgG secondary antibody. Then, an IFN-I reporter cell line 293T stably transfected with a mouse A2 promoter-driven EGFP was used to screen antibody clones that could block human IFNAR1 signaling.
Humanized mice with HIV-1 infection were treated intraperitoneally with anti-IFNAR1 blocking antibodies from 7 to 10 weeks post-infection twice a week at a dose of 400 μg/mouse at the first treatment and 200 μg/mouse for the following treatments. The same dose of mouse isotype IgG2a control was used in all the experiments.
Alternatively, the HIV-1-infected mice were treated with combination antiretroviral therapy (cART) as reported. HIV-1 infected, cART treated mice were treated i.p. With IFNAR1 blocking antibodies from 7 to 10 wpi twice a week with 400 μg/mouse at the first injection and 200 μg/mouse for the following treatments. A same dose of mouse isotype IgG2a control was use in all experiments. Flow cytometry Flurochrome-conjugated antibodies or regents obtained from Biolegend, BD Bioscience, eBioscience and R&D Systems were used in the study.
Live/dead fixable violet dead cell dye (LD7) was purchased from Molecular Probes (Eugene, OR). For humanized mice, live human leukocytes (Y7 -mCD45 -hCD45 +) were analyzed for ILC1 subsets and other cell subsets or phenotypes with CyAn FACS (Dako, Beckman Coulter, Denmark). The data were analyzed with the Summit Software.
For human PBMCs and various tissue-derived lymphocytes, dead cells were excluded using the fixable viability dye eFluor 450 (eBioscience). The remaining live CD45 + cells were analyzed for phenotypic expression with FACS CANTO II, and the data obtained were further analyzed with the FlowJo software (TreeStar, San Carlos, CA). Cytokines, including IL-2, IL-12 and IL-18, were purchased from PeproTech (Rocky Hill, NJ).
For surface marker staining, leukocytes were incubated with antibodies on ice for 30 min and then washed and fixed for further analysis. For staining of HIV-1 gag p24, transcriptional factors, Ki67 and the apoptotic marker active caspase-3, the cells were stained with the surface marker first, and then permeabilized using a Cytofix/Cytoperm kit (BD Bioscience) and stained for intracellular protein. Alternatively, fresh cells were mixed with caspase-1 for 2 h for caspase-1 staining and were then subjected to surface staining. For intracellular cytokine detection, freshly isolated cells were stimulated for 6 h by culturing with PMA (50 ng/ml, Sigma) and ionomycin (1 μM, Merck) in the presence of BFA (1 μM). Alternatively, the cells were incubated with IL-12 (20 ng/ml) plus IL-18 (20 ng/ml) for 12 h, followed by Golgi-stop for an additional 6 h. The cells were then collected for surface marker staining; this was followed by cell permeabilization and intracellular cytokine staining. For CD107a staining, the cells were incubated with anti-CD107a antibodies from the onset of stimulation.
Then, the cells were further incubated with BFA for an additional 6 h. Cell sorting and cell-associated HIV-1 DNA detection Freshly isolated PBMCs from HC and HIV-1-infected patients were enriched for ILCs by depletion of CD3 + T cells, CD14 + monocytes and CD19 + B cells using microbeads (Miltenyi Biotech, Germany). Then, the enriched cells were sorted on a FACSAria II (BD Biosciences). CD4 + ILC1s were isolated by sorting on live cells, singlets, scatter, and lineage -CD56 -CD127 +CD4 + cells (lineage including CD3, CD14, CD16, CD19, CD34, CD11c, CD123, CD117 and CRTH2). CD4 + and CD8 + T cells were directly sorted from PBMCs. Then, nucleic acid was extracted by sorting CD4 + ILC1s, CD4 + T cells and CD8 + T cells using the DNAeasy minikit (Qiagen) to measure total cell-associated HIV-1 DNA. HIV-1 DNA was quantified by real-time PCR according to our previous protocol.
DNA from serial dilutions of ACH2 cells, which contain 1 copy of the HIV-1 genome per cell, was used to generate a standard curve. Apoptosis assays Frozen PBMCs from HCs and HIV-1-infected patients were thawed and cultured in complete RPMI (RPMI 1640 containing 10% heat-inactivated fetal bovine serum, 2 mM l-glutamine, 100 U/ml penicillin and 100 mg/ml streptomycin sulfate) (Cellgro, Manassas, VA) with IL-12 (10 ng/ml), IL-18 (10 ng/ml) and IL-2 (50 IU/ml) for 12 h. Then, the cells were collected to perform in vitro assays. The cells were incubated in the presence of plate-bound anti-CD95 monoclonal antibody or isotype control antibody (5 μg/ml, clone CH11, Millipore) for an additional 24 h. Alternatively, the cells were incubated with 15B mAb conjugated with the toxin sap (15B-sap, 8 ng/ml) to deplete pDCs or with anti-IFN-α/β receptor antibodies (10 μg/ml, Millipore) to block IFN-I signaling for an additional 72 h. Then, the cells were harvested, and the number of live cells was counted and stained for active caspase-3 and/or CD95 expression by ILC1 subsets.
Statistical analysis Data were analyzed using GraphPad Prism software version 5.0 (GraphPad software; San Diego, CA, USA). The data represent the mean ± s.e.m values. One-way ANOVA was used for primary comparisons between different groups, and the result was represented by the overall p value. Secondary comparisons between any two different cohorts of mice or patients were performed using a two-tailed unpaired Student’s t-test. Correlations between variables were evaluated using the Spearman rank-correlation test. Results were considered significant at p values.
S1 Fig Gating strategy for peripheral blood ILC1 subsets. (A) Representative dot plots identify ILC1 subsets.
After gating on lymphocytes (FSC-SSC), singlets, and live CD45 + cells, the cells that remained were identified as lineage -CD127 -CD56 + NK cells and lineage -CD127 +CD56 - total ILC1 cells. Based on CD4 and CD8 expression, ILC1s were further divided into CD4 +CD8 -, CD4 -CD8 + and CD4 -CD8 - ILC1s, while the NK cells did not contain any CD4 +CD8 - cell subpopulations. The lineage markers included CD3, CD14, CD16, CD19, CD123, CD11c, CD34, CD117 (excluding ILC3) and CD294 (CRTH2, excluding ILC2).
The numbers indicate the percentage of cell subsets. (B) A representative histogram shows the expression of TCRαβ, TCRγδ, CD5 and CD94 expression on various ILC1 subsets and NK cells. Shade, isotype control; black curve, markers above. S5 Fig Activation enhances HIV-1 infection in T cells. ( A) Representative dot plots indicate p24 expression within CD3 + T cells present in vitro of mock or HIV-1 NL4-3 stock with or without activation (PHA pre-stimulation for 24 hours). ( B) Summarized data indicate the percentages of p24 + cells within CD3 + T cells in various conditions.
Human PBMCs were first incubated with PHA for 24 hours in the presence of IL-2 (50 IU/ml) and IL-7 (20 ng/ml). The cells were then incubated with HIV/NL4-3 stock or mock stock for additional 4 days. S8 Fig Absence of any effect of HIV-1 infection on the expression of caspase 1 and DR5 by ILC1 subsets.
( A) The representative dot plots depict the expression of caspase 1 on CD4 + and CD4 - ILC1 subsets in the peripheral blood of various groups. The numbers indicate the percentages of cell subsets. ( B) Summary data of caspase 1 expression in peripheral blood CD4 + and CD4 - ILC1s in the HC (n = 15), HIV-1 (n = 27) and HIV-1 plus HAART groups (n = 5). ( C) Representative dot plots depict DR5 expression on CD4 + and CD4 - ILC1 subsets in the peripheral blood of various human patients. The numbers indicate percentages of gated cell subsets. ( D) Summary data of DR5 expression in peripheral blood CD4 + and CD4 - ILC1s in the HC (n = 6), HIV-1 (n = 6) and HIV-1 plus HAART groups (n = 5).
( B and D) Data represent the mean ± s.e.m. S10 Fig The function of ILC-1 in humanized mice with cART and IFNAR blockade. Humanized mice infected with HIV-1 were treated with cART from 4–12 weeks post infection (wpi). From 7 to 10 wpi, the cART-treated mice were injected with α-IFNAR1 antibody or isotype control mIgG2a antibody twice a week.
Mice were terminated at 12wpi. (A) Representative dot plots show the production of IFN-γ and TNF-α by splenic ILC1s from various groups of humanized mice after stimulation with PMA/ionomycin (n = 5 for each group). Numbers indicate the percentages of cytokine-expressing cell subsets. ( B) Summarized data of IFN-γ and TNF-α production in response to PMA/ionomycin of splenic ILC1s from mock, HIV-1-infected mice, HIV-1-infected mice with cART plus mIgG2a isotype antibody or α-IFNAR mAb. Data represent the mean ± s.e.m.
Funding Statement This work was supported in part by grants from the National Natural Science Foundation of China (81672037 to JZ; 91442127, to ZZ; 81471577 to WC; 81571512 to QF), the National Science Fund for Outstanding Young Scholars (81222024 to ZZ), and the UNC University Cancer Research Fund Innovation Grant from the US National Institutes of Health (AI080432, AI077454 and AI095097 to LS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.