Effect of HIV infection and antiretroviral therapy on immune cellular functions.

During chronic HIV infection, immune cells become increasingly dysfunctional and exhausted. Little is known about how immune functions are restored after initiation of antiretroviral therapy (ART). In this study, we assessed cellular and metabolic activity and evaluated the effect of individual antiretrovirals on cellular subsets ex vivo in ART-treated and treatment-naive chronically HIV-infected individuals. We observed that cellular respiration was significantly decreased in most immune cells in chronic HIV infection. The respiration was correlated to immune activation and the inhibitory receptor programmed cell death 1 on CD8+ T cells. ART restored the metabolic phenotype, but the respiratory impairment persisted in CD4+ T cells. This was particularly the case for individuals receiving integrase strand transfer inhibitors. CD4+ T cells from these individuals showed a significant reduction in ex vivo proliferative capacity compared with individuals treated with protease inhibitors or nonnucleoside reverse transcriptase inhibitors. We noticed a significant decrease in respiration of cells treated with dolutegravir (DLG) or elvitegravir (EVG) and a switch from polyfunctional to TNF-α-dominated "stress" immune response. There was no effect on glycolysis, consistent with impaired mitochondrial function. We detected increased levels of mitochondrial ROS and mitochondrial mass. These findings indicate that EVG and DLG use is associated with slow proliferation and impaired respiration with underlying mitochondrial dysfunction, resulting in overall decreased cellular function in CD4+ T cells.

Expansion of Stem Cell-Like CD4+ Memory T Cells during Acute HIV-1 Infection Is Linked to Rapid Disease Progression.

Acute HIV-1 infection is characterized by high viremia and massive depletion of CD4+ T cells throughout all tissue compartments. During this time the latent viral reservoir is established but the dynamics of memory CD4+ T cell subset development, their infectability and influence on disease progression during acute HIV-1 infection has not been carefully described. We therefore investigated the dynamics of CD4+ T cell memory populations in the RV217 (ECHO) cohort during the acute phase of infection. Interestingly, while we found only small changes in central or effector memory compartments, we observed a profound expansion of stem cell-like memory CD4+ T cells (SCM) (2.7-fold; P < 0.0001). Furthermore, we demonstrated that the HIV-1 integration and replication preferentially take place in highly differentiated CD4+ T cells such as transitional memory (TM) and effector memory (EM) CD4+ T cells, while naive and less mature memory cells prove to be more resistant. Despite the relatively low frequency of productively infected SCM, we suggest that their quiescent phenotype, increased susceptibility to HIV-1 integration compared to naive cells and extensive expansion make them one of the key players in establishment and persistence of the HIV-1 reservoir. Moreover, the expansion of SCM in acute HIV-1 infection was a result of Fas upregulation on the surface of naive CD4+ T cells. Interestingly, the upregulation of Fas receptor and expansion of SCM in acute HIV-1 infection was associated with the early viral set point and disease progression (rho = 0.47, P = 0.02, and rho = 0.42, P = 0.041, respectively). Taken together, our data demonstrate an expansion of SCM during early acute HIV-1 infection which is associated with disease outcome.IMPORTANCE Understanding the immunopathology of acute HIV-1 infection will help to develop eradication strategies. We demonstrate here that a CD4+ T cell memory subset expands during acute HIV-1 infection, which is associated with disease progression.

Modulation of Vaccine-Induced CD4 T Cell Functional Profiles by Changes in Components of HIV Vaccine Regimens in Humans.

To date, six vaccine strategies have been evaluated in clinical trials for their efficacy at inducing protective immune responses against HIV infection. However, only the ALVAC-HIV/AIDSVAX B/E vaccine (RV144 trial) has demonstrated protection, albeit modestly (31%; P = 0.03). One potential correlate of protection was a low-frequency HIV-specific CD4 T cell population with diverse functionality. Although CD4 T cells, particularly T follicular helper (Tfh) cells, are critical for effective antibody responses, most studies involving HIV vaccines have focused on humoral immunity or CD8 T cell effector responses, and little is known about the functionality and frequency of vaccine-induced CD4 T cells. We therefore assessed responses from several phase I/II clinical trials and compared them to responses to natural HIV-1 infection. We found that all vaccines induced a lower magnitude of HIV-specific CD4 T cell responses than that observed for chronic infection. Responses differed in functionality, with a CD40 ligand (CD40L)-dominated response and more Tfh cells after vaccination, whereas chronic HIV infection provoked tumor necrosis factor alpha (TNF-α)-dominated responses. The vaccine delivery route further impacted CD4 T cells, showing a stronger Th1 polarization after dendritic cell delivery than after intramuscular vaccination. In prime/boost regimens, the choice of prime and boost influenced the functional profile of CD4 T cells to induce more or less polyfunctionality. In summary, vaccine-induced CD4 T cell responses differ remarkably between vaccination strategies, modes of delivery, and boosts and do not resemble those induced by chronic HIV infection. Understanding the functional profiles of CD4 T cells that best facilitate protective antibody responses will be critical if CD4 T cell responses are to be considered a clinical trial go/no-go criterion.IMPORTANCE Only one HIV-1 candidate vaccine strategy has shown protection, albeit marginally (31%), against HIV-1 acquisition, and correlates of protection suggested that a multifunctional CD4 T cell immune response may be important for this protective effect. Therefore, the functional phenotypes of HIV-specific CD4 T cell responses induced by different phase I and phase II clinical trials were assessed to better show how different vaccine strategies influence the phenotype and function of HIV-specific CD4 T cell immune responses. The significance of this research lies in our comprehensive comparison of the compositions of the T cell immune responses to different HIV vaccine modalities. Specifically, our work allows for the evaluation of vaccination strategies in terms of their success at inducing Tfh cell populations.

Preservation of Peripheral T Follicular Helper Cell Function in HIV Controllers.

The maturation process of high-affinity antibodies is a result of intricate interactions between B cells and follicular helper T (Tfh) cells occurring in lymphoid germinal centers. HIV infection induces significant chronic immune activation, phenotypic skewing, and inflammation driven by years of continuous viral replication. High levels of viremia as well as immune activation and dysfunction have been demonstrated to have a perturbing impact on the B cell memory compartment and contribute to B cell exhaustion. Counterintuitively, the factors associated with perturbation of the B cell compartment seem to be favorable for the generation of highly affinity-matured Env-specific antibodies in a minority of HIV-infected individuals. Thus, the impact of HIV antigenemia on B cells and Tfh cell interactions warrants further exploration. We therefore studied immunophenotypes of HIV-specific B cells in individuals with differing levels of viral control using HIV Env gp120 probes and characterized the functionality of matched T cells in peripheral blood. While CXCR5+ CD4+ T cells were significantly diminished in HIV progressors, we found that a small subset of gp120-specific interleukin-21 (IL-21)-secreting CXCR5+ CD4+ T cells were significantly associated with gp120-specific B cell frequencies. In contrast, neither bulk CXCR5+ CD4+ T cells nor other HIV antigen specificities were associated with gp120-specific B cell levels. HIV-specific B cells derived from elite controllers displayed greater amounts of gp120-specific B cells in the resting memory subset, whereas HIV-specific B cells in progressors accumulated in tissue-like and activated memory subsets. Furthermore, CXCR5+ CD4+ T cells from elite controllers showed a stronger ex vivo capacity to induce B cell maturation and immunoglobulin class switching than cells from HIV progressors.IMPORTANCE Dissecting the factors that are involved in B cell maturation and antibody development is important for HIV vaccine design. In this study, we found that HIV Env-specific CXCR5+ CD4+ T cells that secrete interleukin-21 are strongly associated with B cell memory phenotypes and function. Moreover, we found that the immune responses of HIV controllers showed intrinsically better helper activity than those of HIV progressors.

Circulating HIV-Specific Interleukin-21(+)CD4(+) T Cells Represent Peripheral Tfh Cells with Antigen-Dependent Helper Functions.

A central effort in HIV vaccine development is to generate protective broadly neutralizing antibodies, a process dependent on T follicular helper (Tfh) cells. The feasibility of using peripheral blood counterparts of lymph node Tfh cells to assess the immune response and the influence of viral and vaccine antigens on their helper functions remain obscure. We assessed circulating HIV-specific IL-21(+)CD4(+) T cells and showed transcriptional and phenotypic similarities to lymphoid Tfh cells, and hence representing peripheral Tfh (pTfh) cells. pTfh cells were functionally active and B cell helper quality differed depending on antigen specificity. Furthermore, we found higher frequency of pTfh cells in peripheral blood mononuclear cell specimens from the ALVAC+AIDSVAX (RV144) HIV vaccine trial associated with protective antibody responses compared to the non-protective DNA+Ad5 vaccine trial. Together, we identify IL-21(+)CD4(+) T cells as pTfh cells, implicating them as key populations in the generation of vaccine-evoked antibody responses.

Cooperativity of HIV-Specific Cytolytic CD4 T Cells and CD8 T Cells in Control of HIV Viremia.

UNLABELLED: CD4+ T cells play a pivotal role in the control of chronic viral infections. Recently, nontraditional CD4+ T cell functions beyond helper effects have been described, and a role for cytolytic CD4+ T cells in the control of HIV infection has been suggested. We define here the transcriptional, phenotypic, and functional profiles of HIV-specific cytolytic CD4+ T cells. Fluidigm BioMark and multiparameter flow cytometric analysis of HIV-specific cytolytic CD4+ T cells revealed a distinct transcriptional signature compared to Th1 CD4+ cells but shared similar features with HIV-specific cytolytic CD8+ T cells. Furthermore, HIV-specific cytolytic CD4+ T cells showed comparable killing activity relative to HIV-specific CD8+ T cells and worked cooperatively in the elimination of virally infected cells. Interestingly, we found that cytolytic CD4+ T cells emerge early during acute HIV infection and tightly follow acute viral load trajectory. This emergence was associated to the early viral set point, suggesting an involvement in early control, in spite of CD4 T cell susceptibility to HIV infection. Our data suggest cytolytic CD4+ T cells as an independent subset distinct from Th1 cells that show combined activity with CD8+ T cells in the long-term control of HIV infection. IMPORTANCE: The ability of the immune system to control chronic HIV infection is of critical interest to both vaccine design and therapeutic approaches. Much research has focused on the effect of the ability of CD8+ T cells to control the virus, while CD4+ T cells have been overlooked as effectors in HIV control due to the fact that they are preferentially infected. We show here that a subset of HIV-specific CD4+ T cells cooperate in the cytolytic control of HIV replication. Moreover, these cells represent a distinct subset of CD4+ T cells showing significant transcriptional and phenotypic differences compared to HIV-specific Th1 cells but with similarities to CD8+ T cells. These findings are important for our understanding of HIV immunopathology.

Induction of Gag-specific CD4 T cell responses during acute HIV infection is associated with improved viral control.

UNLABELLED: Effector CD4 T cell responses have been shown to be critically involved in the containment and clearance of viral pathogens. However, their involvement in the pathogenesis of HIV infection is less clear, given their additional role as preferred viral targets. We previously demonstrated that the presence of HIV-specific CD4 T cell responses is somewhat associated with HIV control and that specific CD4 T cell functions, such as direct cytolytic activity, can contribute to control of HIV viremia. However, little is known about how the induction of HIV-specific CD4 T cell responses during acute HIV infection influences disease progression and whether responses induced during the early phase of infection are preferentially depleted. We therefore longitudinally assessed, in a cohort of 55 acutely HIV-infected individuals, HIV-specific CD4 T cell responses from acute to chronic infection. Interestingly, we found that the breadth, magnitude, and protein dominance of HIV-specific CD4 T cell responses remained remarkably stable over time. Moreover, we found that the epitopes targeted at a high frequency in acute HIV infection were recognized at the same frequency by HIV-specific CD4 T cells in chronic HIV infection. Interestingly the induction of Gag-specific CD4 T cell responses in acute HIV infection was significantly inversely correlated with viral set point in chronic HIV infection (R = -0.5; P = 0.03), while the cumulative contribution of Env-specific CD4 T cell responses showed the reverse effect. Moreover, individuals with HIV-specific CD4 T cell responses dominantly targeting Gag over Env in acute HIV infection remained off antiretroviral therapy significantly longer (P = 0.03; log rank). Thus, our data suggest that the induction of HIV-specific CD4 T cell responses during acute HIV infection is beneficial overall and does not fuel disease progression. IMPORTANCE: CD4 T cells are critical for the clearance and control of viral infections. However, HIV preferentially infects HIV-specific CD4 T cells. Thus, their contribution to the control of HIV viremia is uncertain. Here, we study HIV-specific CD4 T cell responses from acute to chronic HIV infection and show that the generation of certain CD4 responses is associated with control rather than disease progression.