The NTP PAC Mixtures Assessment Program (PAC-MAP) provides the framework for assessing a breadth of individual polycyclic aromatic compounds (PACs), defined PAC mixtures, and complex PAC-containing environmental samples using an in vitro/short-term in vivo testing battery that includes a broad spectrum of endpoints. Select PACs have been associated with a wide range of toxicities (carcinogenicity, immunotoxicity, reproductive and developmental toxicity, neurotoxicity) and a complicated array of mechanisms of action. In particular, many PACs have been associated with suppression of humoral immune function and immunotoxicity has been identified as an informative parameter for estimating the carcinogenic potential of PACs. As part of the potential testing battery to predict mixture effects, we have examined the potential for 13 individual PACs and 3 mixtures to modulate the antigen specific antibody response and affect bone marrow cytology. No in vivo immunotoxicology studies were started in FY22 and efforts were focused on data analysis and reporting/archiving of studies conducted in previous contract years. BRT provided 8 final reports for PAC-MAP Immunotoxicity studies in FY22. BRT completed an additional 5 reports for immunopathology studies of the PAC-MAP chemicals. The final report for the immunotoxicity and disease resistances studies of MPEP were also submitted in FY22.