Inhibiting Pd-1 Pathway Rescues Protective Immune Response in Tb Patients: Impact on Bacillary Efflux Pump and Multidrug-Resistance Tb

Abstract

Host T cell response plays a critical role in containment of M. tuberculosis (Mtb) infection by granuloma formation. The prevalence of multidrug-resistance tuberculosis (MDR-TB) among immunocompromised hosts (HIV co-infection & posttransplant patients) indicate the influence of host T cell response on MDR TB. Previously, we have shown critical role of regulatory T (Treg) cells and PD-1 pathway causing suppressed state of T cell response against Mycobacterium tuberculosis (Mtb) among TB patient.In this study, we attempted to understand the status of host immune response among the MDR and Drug Sensitive (DS) TB patients. We also checked the contribution of PD-1 pathway on poly-functional T cells (PFTs), critical for protective immunity in TB. METHODS:For immune response profile and in vitro experiments, polychromatic flowcytometry based immunological assays were performed. PD1 blocking experiments were performed in mice infected with Mtb and invitro model where monocyte derived macrophages (MDM) were infected with virulent Mtb DS strains. Furthermore, the impact of cytokine on the efflux pump of bacteria was evaluated using virulent Mtb DS strains infected MDM in presence of pro and anti-inflammatory cytokines. RESULTS:We observed marked reduction of polyfunctional T cells (PFTs) in TB patients. PFTs could be significantly rescued by blocking PD-1 pathway, which resulted in effective clearance of Mtb in MDM in vitro model. Blocking PD-1 pathway in mice infected with Mtb, demonstrated decrease in Tregs and restoration of PFTs with enhanced reduction of bacillary load in the lung & spleen relative to chemotherapy alone. Among MDR patients, we observed increase in the frequency of Tregs and decrease in frequency of Mtb specific T cell cytokine producers (IFN-g or TNF-a or IFN-gþ TNF-aþ) compared to DS TB patients, suggesting a tight correlation of Treg mediated suppression with MDR status. Furthermore, we observed higher expression of efflux pump in DR strains which could be substantially modulated by pro-inflammatory (IFN-g, TNF-a) and anti-inflammatory cytokines (IL10 and TGF b) in in vitro MDM model. Suppressive cytokines (IL10 and TGF b) increased the efflux pump of Mtb. This is suggestive of possible causal relation of host immune status with the drug efflux pump expression in Mtb. CONCLUSIONS:Our results demonstrate elicitation of weaker effector T cell response in DR TB compared to DS TB patients. Additionally, our findings suggest critical role of PD-1 in suppressing the protective immune response in TB. Rescuing PFTs by blocking PD-1 pathway may offer a novel strategy for adjunct immunotherapy in TB. This may be more relevant in MDR TB as PFT response may modulate the drug pump so as to increase the efficacy of chemotherapy.CLINICAL IMPLICATIONS: Rescuing appropriate immune response may improve the efficacy of anti-tubercular therapy in TB, especially for MDR TB with possible reduction of duration of drug therapy and relapse.