MAP4K1 and cancer: While these data suggest that HPK1 negatively regulates cancer antigen presentation by BMDCs, attribution of its effect on in vivo cancer antigen presentation function to the HPK1 kinase activity could not be made in the studies using HPK1-/- mice since the absence of the HPK1 protein precludes the possibility of BMDCs generating the caspase-cleaved C-terminal fragment known to facilitate apoptosis by blocking the induction of NFκB activation (Brenner et al., 2009).