Dysregulation of mycobacterium tuberculosis and HIV-specific T cell immunity among HIV-tuberculosis co-infected adults from western Kenya.

Abstract

Human immunodeficiency virus (HIV) and Mycobacterium tuberculosis (Mtb) as single infections are clinically manageable. However, their presentation as a co-infection leads to accelerated progression to acquired immunodeficiency syndrome and active tuberculosis. The underlying immunological mechanisms leading to this end-point clinical phenomenon could be associated with dysregulated HIV and Mtb-specific T-cell immunity. This study investigated the changes in T cell frequency, absolute count and phenotype in individuals presenting with Mtb-HIV coinfections, at Jaramogi Oginga Odinga Teaching and referral hospital, the biggest referral facility in western Kenya. Specifically, it determined the effect of Mtb infection and disease on HIV-specific CD4+ and CD8+ T cell immune responses, the effect of HIV on Mtb-specific CD4+ and CD8+ T cell immune responses and evaluated phenotypic expression of selected markers of immune activation and cytotoxicity in individuals with Mtb infection with or without HIV. In this analytical cross-sectional study, a total of 300 participants were screened, 100 enrolled and categorized into 4 groups: 25 with Latent TB infection (LTBI), no HIV, 25 with LTBI and HIV, 25 with active TB and HIV, and 25 with HIV but no form of TB. Approximately 50ml of venous blood was drawn, and peripheral blood mononuclear cells (PBMCs) separated for phenotyping of cell surface molecules and intracellular cytokine staining of T cells by flow cytometry. The frequency, absolute count, and phenotypes of total and antigen-specific CD4+ and CD8+ T cells expressing markers of activation and cytotoxicity were analyzed in response to Mtb Whole Cell Lysate (WCL) and HIV group-specific antigen (gag). Control stimulation conditions included an unstimulated control, Staphylococcus enterotoxin B (SEB), Cytomegalovirus (CMV), and Mycobacterial ESAT6-CFP-10. CD4+ and CD8+ T cell frequencies expressing HLA-DR, CD40L, Ki-67, IFN-γ, Perforin, Granzyme B, CD107a, and Caspase 3 were analyzed using the FACSDiva® version 8.0.1. Flow data was analyzed on FlowJo® version 9. Background subtraction was done and antigen-specific T cells quantified using MIISMOSA software. Mann-Whitney U test was used to test for any significant difference between two groups, while Kruskal Wallis test was used to compare three groups, followed by Dunns pairwise test. Results were considered significant at p≤0.05. The findings showed evidence of depletion of HIV-specific CD4+ and CD8+ T cells in people with ATB, but not LTBI. Expression of HLA-DR, granzyme B, and perforin were increased in total CD4+ and CD8+ T cell populations in individuals with ATB but not HIV-specific CD4+ and CD8+ T cells, which did not differ by Mtb infection and disease status. Furthermore, HIV led to depletion of Mtb-specific CD4+ T cells. IFNγ+ WCL-specific CD4+ T cells (CD40L-IFNγ+) were depleted in both arms with a significant difference (p=0.036), while CD40L+ CD4+ T cells were not. HIV increased immune activation in WCL-specific CD4+ T cells among LTBI individuals. HIV also induced HLADR within Mtb-specific CD4+ T cells in people with LTBI. No significant increase in Ki67 expression was noted. There was no significant difference in expression of the other phenotypic markers (CD38, HLA-DR, Ki67, active caspase-3, granzyme B, and perforin-A) among HIV specific CD4+ and CD8+ T cells. CD40L+ Mtb-specific CD4+ T cell responses were found to predominate in people with and without HIV. These findings suggest that ATB is associated with overall increased T cell activation and cytotoxicity and depletion of HIV-specific CD4+ and CD8+ T cell responses, which may contribute to further impairment of T cell-mediated immune control of HIV replication in the setting of ATB, leading to AIDS. Mtb also leads to depletion of IFN+ cells among people with and without HIV. HIV-associated depletion of Mtb-specific CD4+ T cells suggests that HIV contributes to Mtb T cell-specific dysfunction, leading to active TB. Therefore, interventions targeted toward prevention of progression from LTBI to active TB would be useful among HIV co-infected individuals. They would similarly prevent the progression of HIV to AIDS due to reduced immune activation. Induction of mechanisms that restore functionally depleted T cells, as well reverse the functional impairment, would counter the HIV-induced impairment among co-infected individuals. CD40L+ T cells would offer new frontiers as a new biomarker of immunity in HIV-Mtb co-infection studies. The ability of Mtb and HIV infections to interfere with functional ability of specific T cell immunity points towards the need for early diagnosis and intervention of Mtb and HIV infections, especially in co-infected individuals as this will decrease early progression to ATB and AIDS.