Adiposity As a Principal Component of Lethal Cytokine Storm Following Cancer Immunotherapy in Aged Mice

The use of immunotherapy (IT) in cancer has recently resulted in impressive responses. Yet, their usages, especially those involving cytokine therapies, have also resulted in the induction of severe systemic toxicities often not previously characterized in their preclinical animal studies. Our laboratory has demonstrated that treatment of EL4 lymphoma with a combination immunotherapy consisting of monoclonal agonistic antibody CD40 and IL-2 resulted in significant anti-tumor responses leading to overall increases in survival using young inbred mice (2-6 months of age). Yet, the majority of hematological cancers occur in aged individuals, with most diagnoses occurring past the age of 60. We now demonstrate that systemic immunotherapy administration in aged (>16 months of age), but not young, mice resulted in the induction of a rapid cytokine release syndrome, also known as “cytokine storm”, culminating in multi-organ damage (liver, lung, and gut) leading to rapid lethality by day 2 of treatment. Aging is accompanied by an overall redistribution of body mass, with a decrease in lean muscle mass and increase in adiposity. Similarly, we found that normal aging in inbred mice housed under specific pathogen free conditions was accompanied by increases in visceral fat that was similar to young obese (ob/ob or diet-induced obese [DIO]) mice. We therefore assessed the impact of aging and obesity on inflammatory responses to cancer immunotherapeutics. We determined the effects of increased body fat on systemic immunotherapy tolerance in aged mice compared to young obese mice. Both young ob/ob and DIO generated pro-inflammatory cytokine (ie TNFa and IL6) levels and organ pathologies comparable to aged WT mice following immunotherapy, culminating in rapid lethality after several days of therapy. We observed that young obese mice exhibited greater ratios of M1/M2 macrophages within the peritoneal and visceral adipose tissues and higher percentages of TNFa⁺ macrophages in comparison to young lean mice with immunotherapy. Administration of aCD40/IL-2 with macrophage depletion or TNF-blockade prevented the development of cytokine storms within young obese mice, providing protection from lethality, suggesting that the toxicity was macrophage mediated through increases in TNFa. Calorie-restricted aged mice contain less visceral fat and upon aCD40/IL-2 administration displayed reduced cytokine levels, protection from organ pathology, and protection from lethality. Our data demonstrates adiposity as a critical factor in the age-associated inflammatory pathologic responses to systemic anti-cancer immunotherapy and may have a significant impact when immunotherapy is used clinically within cancer therapy regimens. These data also underscore the critical importance of taking aging and body fat into consideration with preclinical assessments.