IMMUNOPHENOTYPE, MOLECULAR DIAGNOSIS, MINIMAL RESIDUAL DISEASE, AND MULTIDRUG RESISTANCE PROTEIN EXPRESSION IN MODIFIED COP, MODIFIED CHOP AND RESCUE PROTOCOLS OF TREATED CANINE LYMPHOMAS
Authors:   , Sirivisoot Sirintra 
Published: September 2023

Multicentric lymphoma is the most common hematopoietic tumors in dogs. Both B- or T-lymphocyte clones can originate to lymphoma. A gold standard method to differentiate each lymphocyte lineage is immunohistochemistry (IHC) by detecting specific proteins of B and T cell. A protein marker for T and B cells is CD3 and CD79a, respectively. However, another pan pre B-cell marker is Pax5 or B-cell specific activator protein. It is more specific and sensitive than CD79a because it expresses only in B-cell lymphoma cases. The first purpose of this research was to 1) determine Pax5 expression in canine lymphomas by IHC and compare the results to CD79a and CD3 expression for lymphoid lineage. The result of this study showed that 28 B-cell lymphoma cases expressed both Pax5 and CD79a, nevertheless four cases of B cell illustrated only Pax5 expression. Furthermore, four from ten T-cell lymphoma samples presented dual CD3 and CD79 expression. Therefore, Pax5 has 100% sensitivity and specificity, whereas CD79a has 87.5% sensitivity and 71.4% specificity. Immunocytochemistry (ICC) is easier and cheaper than IHC for immunophenotyping. Clonality assay or PCR for antigen receptor rearrangement (PARR) could diagnose neoplastic lymphocyte clones and additionally detect minimal residual disease (MRD) in canine lymphomas. The second aim of this research was to 2) develop heteroduplex PARR for clonality test from peripheral blood and lymph node cytology and develop ICC for lineage determination compared to IHC using Pax5 and CD3. Immunophenotyping results by ICC and IHC with both Pax5 and CD3 showed strong correlation in 25 samples of B-cell lymphoma and three samples of T-cell lymphomas. When compared the clonality results between heteroduplex PARR and IHC, the percentage agreement was 60%. Thus, heteroduplex PARR could be used as an adjunctive method with IHC or ICC. Canine multicentric lymphoma generally responds well to chemotherapy, but tumor relapse after complete remission is prevalent because of MRD. MRD could assess by only molecular techniques. The third objective of this research was to 3) evaluate MRD from peripheral blood using heteroduplex PARR in canine multicentric B- and T-cell lymphomas during treatment with modified L-COP (L-asparaginase, vincristine, cyclophosphamide, and prednisolone)) and modified L-CHOP (L-asparaginase, vincristine, cyclophosphamide, doxorubicin and prednisolone) for determining treatment efficacy and treatment response between two protocols. MRD negative results showed the correlation to complete remission during treatment and could be useful for predicting treatment efficacy and clinical response. Drug resistance mechanisms is a major cause of treatment failure during treatment or after complete remission in refractory and relapsing canine lymphoma because tumor cells upregulate multidrug resistance protein for efflux toxic drugs out of cells. Two multidrug resistance proteins that have a role in drug resistance mechanism in canine multicentric B- and T-cell lymphoma are P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP). Furthermore, tyrosine kinase inhibitor (TKI) could inhibit Pgp function. The final aim of this research was to 4) develop rescue protocol for refractory/relapsed canine lymphoma with lomustine (CCNU) or L-asparaginase and vincristine concurrent with toceranib phosphate, and asses protein expression levels of Pgp and BCRP from peripheral blood before and after treatment using qRT-PCR. The results showed that toceranib phosphate or TKI with CCNU or L-asparaginase and vincristine tended to decrease the transcription expression levels of Pgp and BCRP when compared the levels prior to and after treatment. Hence, this rescue protocol could be another treatment option in refractory/relapsed canine lymphomas.