Capillary-leak syndrome: an unrecognized early immune adverse effect of checkpoint-inhibitors treatment

Capillary-leak syndrome is strongly associated with cytokine activity states. It is an ill-recognized adverse effect of checkpoint inhibitors treatment, which are typically associated with cellular immune response. We describe two patients with capillary leak syndrome following immune checkpoint inhibitors treatment. We present linking mechanisms between checkpoint inhibitors, cellular immunity, cytokine action and endothelial damage. We suggest that capillary-leak syndrome is a unique adverse effect of immunotherapy, resulting from complex interactions between cellular and cytokine activation and that its expression is probably depending on inherent host immune variabilities.