Abstract A015: Immunoglobulinheavy chain variable region gene mutational status in chronic lymphocytic leukemia patients in Nigeria

Abstract

Chronic lymphocytic leukemia (CLL) is an indolent B-cell lymphoid neoplasm characterized by the clonal expansion of CD5/CD23/CD19 and CD20-positive positive B-cells in blood, bone marrow and lymphoid tissues. It is commonly seen in the Western world compared to sub-Saharan African regions. The mutational status of the immunoglobulin heavy chain variable region (IGH) genes is a prognostic feature in CLL. The aims are to identify the most used alleles of the variable (V) diversity (D) and joining (J) gene segments of the IGH gene, to analyze complementarity determining region 3 (CDR3) properties and the mutational status of the IGH in CLL. We analyzed IGH genes’ mutational status by performing the sequencing of 8 Nigerian CLL patients out of 23 CLL cases obtained from three centers namely, University College Hospital, Ibadan, Oyo State, Enugu State University of Science and Technology Teaching Hospital (ESUTH), and Meena Histopathology and Cytology Laboratory, Jos, Plateau State. Diagnosis of CLL was confirmed according to the latest World Health Organisation (WHO) classification in our previous study. The samples were subjected to polymerase chain reaction (PCR) amplification of the IGH locus using the BIOMED-2 protocol. The research approvals were obtained from the University of Nigeria Teaching Hospital, Enugu (UNTH-NHREC/05/ 01/2008B), Ministry of Health, Ibadan, Oyo State (AD13/479/1138), and Meena Histopathology and Cytology Laboratory, Jos, Plateau State (MEENALAB/AEC/ 177). Of the 23 cases, 8 (30.4%) cases were amplifiable and showed common clonal origin using the FR1 primer mixes (BIOMED-2 protocol). The ages of the patients with the sequenced cases ranged from 50-78 years, with three females and four males. Most of the specimens were from nodal sites although two cases were from extranodal sites, namely the colon and the omentum. Clinical information on patients regarding the disease's staging, treatment, and overall survival were not available. The IGH analysis revealed the frequent usage of the IGHV4-34 allele (38%) for the V gene segment, IGHD6-13 (43%) for the D gene segment and IGHJ4-02 allele (43 %) for the J gene segment. The mutational analysis revealed that 62.5% of the CLL cases had mutated IGH and this occurred more within the older age bracket. The complementarity determining region (CDR3) properties showed a median length of 13 amino acids and longer CDR3 lengths were recorded in unmutated cases as opposed to mutated cases (P=0.002). The study demonstrated a higher prevalence of IGHV4-34 gene usage of the IGH in Nigerian CLL patients and more of mutated IGH than unmutated IGH which is indicative of favourable prognostic feature in the studied Nigerian cases.