Mycobacterium tuberculosis-specific CD8+ T cell recall in convalescing TB subjects with HIV co-infection

Mycobacterium tuberculosis-Human Immunodeficiency Virus Infection and the Role of T Cells in Protection

Tuberculosis (TB), primarily caused by Mycobacterium tuberculosis (M. tb), remains a widespread fatal health issue that becomes significantly detrimental when coupled with HIV. This study explores the host's innate and adaptive immune system response to TB in HIV immunocompromised patients, highlighting the significant role of CD8+ T cells. While the crucial role of macrophages and cytokines, like TNF-α and IFN-γ, in managing the host's immune response to M. tb is examined, the emphasis is on the changes that occur as a result of HIV coinfection. With the progression of HIV infection, the primary source of IFN-γ changes from CD4+ to CD8+ T cells, especially when latent TB advances to an active state. This study sheds light on the necessity of developing new preventative measures such as vaccines and new treatment approaches to TB, especially for immunocompromised patients, who are at a higher risk of life-threatening complications due to TB-HIV coinfection.

Evaluation of tuberculosis diagnostic biomarkers in immunocompromised hosts based on cytokine levels in QuantiFERON-TB Gold Plus

Tuberculosis (TB) remains a serious health concern globally. QuantiFERON-TB (QFT) is a diagnostic tool for TB detection, and its sensitivity is reduced in immunocompromised hosts with low T lymphocyte counts or abnormal T cell function. This study aimed to evaluate the correlation between T cell and cytokine levels in patients with active TB using QFT-Plus. Forty-five patients with active TB were enrolled, and the cytokines in QFT-Plus tube supernatants were quantified using the MAGPIX System. CD4⁺ T cell count negatively correlated with patient age (p < 0.001, r = -0.51). The levels of TB1-responsive interleukin-1 receptor antagonist (IL-1Ra) and IL-2 correlated with CD4⁺ T cell count, whereas the levels of TB2-responsive IL-1Ra and IFN-γ-induced protein 10 correlated with both CD4⁺ and CD8⁺ T cell counts. Cytokines that correlated with CD4⁺ and CD8⁺ T cell counts might not be suitable TB diagnostic biomarkers in immunocompromised hosts. Notably, cytokines that did not correlate with the T cell counts, such as monocyte chemoattractant protein-1, might be candidate biomarkers for TB in immunocompromised hosts. Our findings might help improve TB diagnosis, which could enable prompt treatment and minimize poor disease outcomes.

Fourth-Generation QuantiFERON-TB Gold Plus: What Is the Evidence?

QuantiFERON-TB Gold Plus (QFT-Plus) is the latest generation of interferon gamma release assays (IGRAs) to receive approval from the U.S. FDA, replacing its predecessor, QuantiFERON-TB Gold In-Tube (QFT-GIT). The novelty of QFT-Plus is that it elicits a response from CD8 T cells, in addition to CD4 T cells, thus collecting a broader response from T-cell subsets than QFT-GIT. It was developed with the aim to improve the detection of latent tuberculosis infection (LTBI), especially among recently exposed contacts, immunocompromised hosts, and young children. In this minireview, we summarize the performance of QFT-Plus compared with that of QFT-GIT among active tuberculosis (TB) patients (a surrogate for LTBI patients), high-risk populations, and low-risk individuals based on recent publications. Studies comparing QFT-Plus to QFT-GIT currently do not support the superior performance of QFT-Plus in individuals with active TB and LTBI. The difference in sensitivity between QFT-Plus and QFT-GIT in active TB patients was not significant in nearly all studies and ranged from -4.0 to 2.0%. Among high-risk groups, the agreement between QFT-Plus and QFT-GIT was 89.9 to 96.0% (kappa coefficient range, 0.80 to 0.91). The specificity in the low-risk population was slightly lower for QFT-Plus than for QFT-GIT, with the difference ranging from -7.4 to 0%. Further studies are needed to accurately evaluate the sensitivity of QFT-Plus in immunocompromised hosts and children. In addition, further evidence is required to validate a modified interpretation of QFT-Plus for the identification of false-positive results in low-risk health care workers.

Specificity of QuantiFERON-TB Plus, a New-Generation Interferon Gamma Release Assay

Interferon gamma release assays (IGRAs) are important tools in identifying prior tuberculosis exposure. The new-generation QuantiFERON-TB Gold Plus (QFT-Plus) assay, recently approved for use in the United States, differs from the current-generation QFT Gold-In-Tube (QFT-GIT) assay with the addition of a second antigen tube that also contains novel CD8⁺ T-cell-stimulating peptides. The QFT-Plus assay has increased sensitivity in immunocompromised populations, and we sought to assess the specificity of QFT-Plus compared to that of QFT-GIT in low-risk individuals. We enrolled adults without tuberculosis risk factors, including a subgroup with pulmonary nontuberculous mycobacterial (NTM) disease due to Mycobacterium avium complex (MAC) or Mycobacterium abscessus. The primary outcome measures included specificity, interassay concordance, and agreement between the QFT-Plus and QFT-GIT assays. Of 262 participants enrolled, 51 had pulmonary NTM. The median age was 39 years (age range, 18 to 78 years); 73% were female. Among the 262 individuals who were enrolled, 5 (1.9%) individuals had positive QFT-Plus results, and 3 of these individuals also had positive QFT-GIT results. The two individuals with discordant results (QFT-Plus positive/QFT-GIT negative) had only one tube positive in the QFT-Plus assay. The overall specificity of QFT-Plus and QFT-GIT was 98.1% (95% confidence interval [CI], 95.6, 99.4%) and 98.9% (95% CI, 96.7, 99.8%), respectively. The QFT-Plus specificity was similar in both the NTM (98.0% [95% CI, 89.4, 99.9%]) and non-NTM (98.1% [95% CI, 95.2, 99.5%]) groups. QFT-Plus has a high specificity, similar to that of the QFT-GIT assay, including in patients with pulmonary MAC or M. abscessus disease.

Pulmonary Tuberculosis in Humanized Mice Infected with HIV-1

Co-infection with HIV increases the morbidity and mortality associated with tuberculosis due to multiple factors including a poorly understood microbial synergy. We developed a novel small animal model of co-infection in the humanized mouse to investigate how HIV infection disrupts pulmonary containment of Mtb. Following dual infection, HIV-infected cells were localized to sites of Mtb-driven inflammation and mycobacterial replication in the lung. Consistent with disease in human subjects, we observed increased mycobacterial burden, loss of granuloma structure, and increased progression of TB disease, due to HIV co-infection. Importantly, we observed an HIV-dependent pro-inflammatory cytokine signature (IL-1β, IL-6, TNFα, and IL-8), neutrophil accumulation, and greater lung pathology in the Mtb-co-infected lung. These results suggest that in the early stages of acute co-infection in the humanized mouse, infection with HIV exacerbates the pro-inflammatory response to pulmonary Mtb, leading to poorly formed granulomas, more severe lung pathology, and increased mycobacterial burden and dissemination.

[Morphological characteristics of inflammation in HIV-associated pulmonary tuberculosis with regard to the expression of myeloperoxidase]

OBJECTIVE

to characterize the morphological features of inflammation and the degree of myeloperoxidase expression in the lung of patients who died from HIV-associated tuberculosis (TB).

MATERIAL AND METHODS

Autopsy lung tissue specimens from 229 patients with HIV-associated TB were examined. A comparison group consisted of dead TB mono-infected patients (n = 30). Dead HIV/TB co-infected patients were divided into subgroups: 1) 50 patients with Stage 4A-4B and a CD4(+)-lymphocyte count of more than 200 cells/µl; 2) 54 with Stage 4B-4C and a CD4(+)-lymphocyte count of 100 to 200 cells/µl; 3) 125 with Stage 4C-5 and a CD4(+)-lymphocyte count of less than 100 cells/µl. Histological and immunohistochemical examinations of lung slices were performed using antibodies to myeloperoxidase (MPO).

RESULTS

The predominant types of an inflammatory response were revealed according to the level of CD4+ lymphocytes. The lungs in Subgroup 1 showed a predominant typical granulomatous response (82%). Subgroup 2 exhibited an exudative-productive inflammatory response (57.4%) while Subgroup 3 displayed an alterative necrotic type (92.8%). Subgroup 3 showed the most marked reduction in lymphocyte numbers in the areas of inflammation, which was accompanied by a significant increase in the relative density and other morphometric parameters of MPO-positive macrophages and granulocytes in the inflammatory infiltration zones and alveolar walls.

CONCLUSION

The identified changes in the lungs suggest that there is a decline in the magnitude of a delayed type hypersensitivity reaction, a progression of alterative necrotic processes as CD4(+) lymphocytes decrease in the systemic blood flow, and an increase in the proportion of functionally immature macrophages in the areas of inflammation, which reflects a substantially impaired local immune response to the persistence of M. tuberculosis in HIV infection.

HIV-TB coinfection impairs CD8(+) T-cell differentiation and function while dehydroepiandrosterone improves cytotoxic antitubercular immune responses

Tuberculosis (TB) is the leading cause of death among HIV-positive patients. The decreasing frequencies of terminal effector (TTE ) CD8(+) T cells may increase reactivation risk in persons latently infected with Mycobacterium tuberculosis (Mtb). We have previously shown that dehydroepiandrosterone (DHEA) increases the protective antitubercular immune responses in HIV-TB patients. Here, we aimed to study Mtb-specific cytotoxicity, IFN-γ secretion, memory status of CD8(+) T cells, and their modulation by DHEA during HIV-TB coinfection. CD8(+) T cells from HIV-TB patients showed a more differentiated phenotype with diminished naïve and higher effector memory and TTE T-cell frequencies compared to healthy donors both in total and Mtb-specific CD8(+) T cells. Notably, CD8(+) T cells from HIV-TB patients displayed higher Terminal Effector (TTE ) CD45RA(dim) proportions with lower CD45RA expression levels, suggesting a not fully differentiated phenotype. Also, PD-1 expression levels on CD8(+) T cells from HIV-TB patients increased although restricted to the CD27(+) population. Interestingly, DHEA plasma levels positively correlated with TTE in CD8(+) T cells and in vitro DHEA treatment enhanced Mtb-specific cytotoxic responses and terminal differentiation in CD8(+) T cells from HIV-TB patients. Our data suggest that HIV-TB coinfection promotes a deficient CD8(+) T-cell differentiation, whereas DHEA may contribute to improving antitubercular immunity by enhancing CD8(+) T-cell functions during HIV-TB coinfection.