Intravesical administration of Bacillus Calmette-Guérin (BCG) was one of the first FDA-approved immunotherapies and remains a standard treatment for bladder cancer. Previous studies have demonstrated that intravenous (IV) administration of BCG is well-tolerated and effective in preventing tuberculosis infection in animals. Here, we examine IV BCG in several preclinical lung tumor models. Our findings demonstrate that BCG inoculation reduced tumor growth and prolonged mouse survival in models of lung melanoma metastasis and orthotopic lung adenocarcinoma. Moreover, IV BCG treatment was well-tolerated with no apparent signs of acute toxicity. Mechanistically, IV BCG induced tumor-specific CD8⁺ T cell responses, which were dependent on type 1 conventional dendritic cells, as well as NK cell-mediated immunity. Lastly, we also show that IV BCG has an additive effect on anti-PD-L1 checkpoint inhibitor treatment in mouse lung tumors that are otherwise resistant to anti-PD-L1 as monotherapy. Overall, our study demonstrates the potential of systemic IV BCG administration in the treatment of lung tumors, highlighting its ability to enhance immune responses and augment immune checkpoint blockade efficacy.

Several hundred millions of people have been diagnosed of coronavirus disease 2019 (COVID-19), causing millions of deaths and a high socioeconomic burden. SARS-CoV-2, the causative agent of COVID-19, induces both specific T- and B-cell responses, being antibodies against the virus detected a few days after infection. Passive immunization with hyperimmune plasma from convalescent patients has been proposed as a potentially useful treatment for COVID-19. Using an in-house quantitative ELISA test, we found that plasma from 177 convalescent donors contained IgG antibodies specific to the spike receptor-binding domain (RBD) of SARS-CoV-2, although at very different concentrations which correlated with previous disease severity and gender. Anti-RBD IgG plasma concentrations significantly correlated with the plasma viral neutralizing activity (VN) against SARS-CoV-2 in vitro. Similar results were found using an independent cohort of serum from 168 convalescent health workers. These results validate an in-house RBD IgG ELISA test in a large cohort of COVID-19 convalescent patients and indicate that plasma from all convalescent donors does not contain a high enough amount of anti-SARS-CoV-2-RBD neutralizing IgG to prevent SARS-CoV-2 infection in vitro. The use of quantitative anti-RBD IgG detection systems might help to predict the efficacy of the passive immunization using plasma from patients recovered from SARS-CoV-2.

Background: Intravesical BCG is the gold-standard therapy for non-muscle invasive bladder cancer (NMIBC); however, it still fails in a significant proportion of patients, so improved treatment options are urgently needed. Methods: Here, we compared BCG antitumoral efficacy with another live attenuated mycobacteria, MTBVAC, in an orthotopic mouse model of bladder cancer (BC). We aimed to identify both bacterial and host immunological factors to understand the antitumoral mechanisms behind effective bacterial immunotherapy for BC. Results: We found that the expression of the BCG-absent proteins ESAT6/CFP10 by MTBVAC was determinant in mediating bladder colonization by the bacteria, which correlated with augmented antitumoral efficacy. We further analyzed the mechanism of action of bacterial immunotherapy and found that it critically relied on the adaptive cytotoxic response. MTBVAC enhanced both tumor antigen-specific CD4⁺ and CD8⁺ T-cell responses, in a process dependent on stimulation of type 1 conventional dendritic cells. Importantly, improved intravesical bacterial immunotherapy using MBTVAC induced eradication of fully established bladder tumors, both as a monotherapy and specially in combination with the immune checkpoint inhibitor antiprogrammed cell death ligand 1 (anti PD-L1). Conclusion: These results contribute to the understanding of the mechanisms behind successful bacterial immunotherapy against BC and characterize a novel therapeutic approach for BCG-unresponsive NMIBC cases.

Bacille Calmette–Guérin (BCG) is the only licensed vaccine against tuberculosis (TB) but provides inconsistent protection against disease. Studies in non-human primates show that intravenous BCG confers superior protection compared to intradermal vaccination, yet how different vaccination routes reprogram lung immunity in mice - the primary model for mechanistic studies - remains incompletely defined at single cell or spatial resolution. Moreover, while lung macrophages are key effectors during Mycobacterium tuberculosis infection, most studies have focused on alveolar macrophages, leaving interstitial macrophage responses to vaccination largely unexplored. Here, we define the cellular and spatial immune landscape shaped by three BCG vaccination routes in mice using flow cytometry, single-cell RNA sequencing, and spatial transcriptomics. Comparing intratracheal (IT), intravenous (IV), and subcutaneous (SC) vaccination, we demonstrate that mucosal IT delivery uniquely reprograms interstitial macrophages, establishes spatially organized immune hubs with CD4 T cells, and provides superior protection against infectious challenge. These findings identify IM as key mediators of mucosal vaccine-induced protection and provide a framework for the rational optimization of vaccines against respiratory pathogens.