Generally speaking, CD22 is a regulatory molecule that prevents the overactivation of the immune system and the development of autoimmune diseases.

Together, this implies that CD22 interacting with trans ligands is crucial for the homing of mature, recirculating B cells to the bone marrow.

[10] The intracellular part of CD22 consists of 6 tyrosine residues which contain both ITIM and ITAM motifs suggesting both inhibitory and activation role in signaling.

Phosphorylation is mediated by Lyn, a protein tyrosine kinase (PTK) of the Src family found in lipid rafts.

[9] After CD22 is phosphorylated, the ITIM motifs provide docking sites for the SH2 domain containing protein tyrosine phosphatase called SHP-1.

Specifically, mutations in the sialic acid esterase were frequently found in patients with rheumatoid arthritis and SLE.

[16] Moxetumomab pasudotox is approved in the EU and USA for treatment of relapsed or refractory hairy cell leukemia.

The reason is that CD22 is rapidly internalized rather than being exposed to the extracellular environment making it more suitable for specific delivery of these conjugates.

[19] One of such therapeutics is inotuzumab, which was approved by the FDA for the treatment of relapsed or refractory B cell acute lymphoblastic leukemia in August 2017.