Anti–PD-1 Antibody Treatment Promotes Clearance of Persistent Cryptococcal Lung Infection in Mice

Abstract

Activation of immunomodulatory pathways in response to invasive fungi can impair clearance and promote persistent infections. The Programmed Cell Death Protein-1 (PD-1) signaling pathway inhibits immune effector responses against tumors and immune checkpoint inhibitors that block this pathway are being increasingly used as cancer therapy. The objective of the current study was to investigate whether this pathway contributes to persistent fungal infection and to determine whether anti-PD-1 antibody treatment improves fungal clearance. Studies were performed using C57BL/6 mice infected with a moderately virulent strain of Cryptococcus neoformans (52D) which resulted in prolonged elevations in fungal burden and histopathologic evidence of chronic lung inflammation. Persistent infection was associated with increased and sustained expression of PD-1 on lung lymphocytes, including a mixed population of CD4+ T cells. In parallel, expression of the PD-1 ligands, PD-L1 and PD-L2, was similarly upregulated on specific subsets of resident and recruited lung dendritic cells and macrophages. Treatment of persistently-infected mice for four weeks by repetitive administration of neutralizing anti-PD-1 antibody significantly improved pulmonary fungal clearance. Treatment was well tolerated without evidence of morbidity. Immunophenotyping revealed that anti-PD-1 antibody treatment did not alter immune effector cell numbers or myeloid cell activation. Treatment did reduce gene expression of IL-5 and IL-10 by lung leukocytes and promoted sustained upregulation of OX40 by Th1 and Th17 cells. Collectively, this study demonstrates that PD-1 signaling promotes persistent cryptococcal lung infection and identifies this pathway as a potential target for novel immune-based treatments of chronic fungal disease.

B Cell Compartmentalization in Blood and Cerebrospinal Fluid of HIV-Infected Ugandans with Cryptococcal Meningitis

“…Moreover, the altered PD-1 role with PD-1 antibody blocker in mouse cryptococcosis infection improved host survival. The improved survival was associated with the downregulation of immune regulatory responses (IL-10 and IL-5), enhanced expression of proinflammatory cytokine responses (Th1/Th17 balance), and increased fungal clearance (52). In summary, the role of PD-1 expression and altered cellular functions are demonstrated to be similar in a spectrum of cells in diseased hosts.…”

Contribution of IL-1RI Signaling to Protection against Cryptococcus neoformans 52D in a Mouse Model of Infection

“…To characterize the effect of IL-1RI signaling on the cellular immune response after C. neoformans infection, flow cytometry analysis of whole-lung digests was performed on WT and IL-1RI −/− mice at serial time points postinfection. A comprehensive gating strategy was used for the identification of resident and recruited myeloid cell subsets (Figure 4 ) ( 42 – 44 ). Prior to infection, no significant difference was observed in the total number of lung leukocytes between the two strains.…”

“…No significant difference in the percentage of pDCs, CD103 + DCs, and CD11b + cDCs was observed in the lungs of BALB/c and IL-1R −/− mice after C. neoformans 52D infection; however, at day 21 postinfection, there was a significantly higher percentage and number of AMs in BALB/c compared to IL-1R −/− mice (Figures 6 A,B,D). As both monocyte-derived ExMs and DCs are CD11b + , CD11c + , CD24 − , MHCII + , and CD64 + , we used autofluorescence to distinguish macrophages from DCs ( 42 , 45 , 47 ) (Figure 4 ). This analysis showed comparable recruitment of both cell types between the two strains at day 7 postinfection; however, WT mice had a significantly higher number of inflammatory DCs (days 14 and 21) and ExMs (day 21) compared to IL-1RI −/− mice (Figures 6 C,E).…”

“…Classically activated macrophages (M1) that express high levels of pro-inflammatory cytokines and costimulatory molecules, produce high levels of reactive nitrogen and oxygen intermediates, and promote strong IL-12-mediated Th1 responses are efficient killers of C. neoformans . In contrast, alternatively activated macrophages (M2) that express chitinase-like 3 (Ym1), found in inflammatory zone (FIZZ1), mannose receptor (CD206), and arginase-1 (Arg1), have reduced pro-inflammatory cytokine secretion and are less microbicidal ( 3 , 9 , 42 , 43 , 47 , 49 – 53 ). As the number of recruited macrophages peaked at day 14 postinfection in both strains, we characterized polarization at this time point using iNOS and CD206 as representative markers for M1 and M2 macrophages, respectively.…”

Animal Models of Cryptococcus neoformans in Identifying Immune Parameters Associated With Primary Infection and Reactivation of Latent Infection

“…Differently from humans, rabbits, and rats (92, 94, 101-105), mice do not produce a granulomatous response against highly virulent C. neoformans strains, and they eventually succumb to the infection. Investigators have utilized less virulent strains, such as C. neoformans strain 52D, in which mice develop a persistent infection with a granulomatous response after intranasal infection (106)(107)(108)(109)(110). This model has allowed researchers to study chronic cryptococcosis and brain dissemination in mice, although there are several drawbacks to using less virulent strains that include induction of immunity not normally associated with highly virulent strains.…”