Correlations between reduced HPK1 expression levels and autoimmune diseases such as systemic lupus erythematosus (Zhang et al., 2011) and psoriatic arthritis (Zhou et al., 1999) have been reported, but there is no direct evidence to suggest that these individuals have enhanced anti-tumor immune responses due to decreased HPK1 protein levels. This evidence concerns the gene MAP4K1 and psoriatic arthritis.