PTPN22 and B-cell chronic lymphocytic leukemia: Furthermore, additional studies will be required to determine whether lymphoid tyrosine phosphatase (Lyp) also known as PTPN22, whose expression was reported to be increased in CLL B cells, plays a role in the response of CLL B cells to therapeutic agents (Negro et al., Blood (ASH Annual Meeting Abstracts) 2009 114: Abstract 800).