IL2 and neoplasm: Furthermore, the S spacer CAR T cell-treated group showed an increase in the levels of human IL-2 and TNFα in peripheral blood, as demonstrated in Figure 4B. Taken together, these findings suggested that targeting SSEA-4 in vivo resulted in significant on-target/off-target tumor toxicities, whereby the S spacer CAR T cell treatment conferred the highest degree of toxicity.