Practical Implementation:

CAL2 labels the megakaryocytes in myeloproliferative neoplasms (essential thrombocythaemia (ET) and primary myelofibrosis (PMF)) with CALR mutation and enables to distinguish ET and PMF with CALR mutation from polycythemia vera (PV), from CALR mutation negative ET and PMF and from reactive bone marrow.

Why is CAL2 able to detect all known types of CALR mutations?

All types of CALR mutation result in a novel C-terminus. This harbors a common epitope expressed in all kinds of CALR mutations. The CAL2 antibody is directed against this common epitope. Therefore, it can be concluded that the CAL2 antibody is able to detect all CALR mutations.

CAL2 IHC of four PMF cases:

A and C: Selective staining of mutated CALR protein in megakaryocytes of two PMF cases, respectively in prefibrotic phase and in fibrotic phase, in which Sanger sequencing detected a CALR mutation.

B and D: Absent CAL2 staining in two PMF cases, respectively in prefibrotic and in fibrotic phase, both without molecularly detected mutated CALR. The fibrotic stroma remains unstained (C and D).

A

B

C

D

References

1. Bonifacio M et al. CAL2 Monoclonal Antibody Is a Rapid and Sensitive Assay for the Detection of Calreticulin Mutations in Essential Thrombocythemia and May Provide Prognostic Informations. BLOOD 128: 3122, 2016
2. Nomani L et al. CAL2 Immunohisto-chemical Staining Accurately Identifies CALR Mutations in Myeloproliferative Neoplasms. Am J Clin Pathol. 146(4): 431-438, 2016.
3. Andrici J et al. Mutation specific immuno-histochemistry is highly specific for the presence of calreticulin mutations in myeloproliferative neoplasms. Pathology 48(4): 319-324, 2016
4. Stein, H et al. A new monoclonal antibody (CAL2) detects CALRETICULIN mutations in formalin-fixed and paraffin embedded bone marrow sections. Leukemia 2015, accepted for publication.
5. Nangalia J et al. Somatic CALR Mutations in Myeloproliferative Neoplasms with Nonmutated JAK2. N Engl J Med 369(25): 2391-2405, 2013.
6. Klampfl T et al. Somatic Mutations of Calreticulin in Myeloproliferative Neoplasms. N Engl J Med 369(25): 2379-2390, 2013.