Killer Cell Immunoglobulin-like Receptor Profile in Acute Myeloid Leukemia with Heterogenous Cytogenetic Abnormalities and Its Association with Clinical Outcome

Introduction: Acute myeloid leukemia (AML) is associated with heterogeneous cytogenetic abnormalities which contributes towards biology and prognosis of the disease. Natural killer (NK) cells are the first line of defense against tumor cells. NK cells interact with AML cells via multiple receptors including killer cell immunoglobulin-like receptor (KIR). Evidence of susceptibility of AML cells to NK cells in the context of KIR-ligand mismatch NK immunotherapy has suggested a role of KIR repertoire in the development and clinical outcome of AML. The aim of this study is to determine the KIR profile of AML patients with different cytogenetic abnormalities and to evaluate its association with clinical outcome.

Methods: Peripheral blood was collected from patients diagnosed with AML after informed consent in accordance with Declaration of Helsinki and approved from Ethical Review Board of Aga Khan University. Peripheral blood mononuclear cells were isolated and subjected to genomic DNA extraction. KIR genotyping was performed by polymerase chain reaction using sequence-specific primers (Vilches et al, Tissue Antigens 2007). Relationship between KIR loci in AML and healthy individuals was compared using chi-square test. Statistical analysis was performed using SPSS statistics (version 26) and a p value of <0.05 was considered statistically significant.

Results: KIR genotyping was performed on 35 cases of AML with mean age of 39 years (range:16-58). Number of male and female patients was 25 and 10 respectively. We found 3 (8.57%) patients with AA KIR haplotype while 33 (91.42%) patients showed Bx haplotype (Figure 1). All the patients with AA haplotype harbored t(15;17) (q22; q21) which has a favorable prognosis while patients with Bx KIR haplotype showed cytogenetic abnormalities with favorable, intermediate, and adverse prognosis.

The B-content score of patients with Bx KIR haplotype (n=32) was scored from 1 to 4 based on the total sum of B loci (Cooley et al, Blood 2010). We found that majority of cases had a B-content score of 2 (53.12%) while 7 (21.87%), 6(18.75%) and 2 (6.25%) patients had a score of 1, 3 and 4 respectively. Cytogenetic profile associated with favorable, intermediate, and adverse prognostic risk was found in all groups of patients irrespective of B-content score (Table 1). A standard induction treatment was given to 26 patients with Bx KIR haplotype. Around 67% of patients with B-content score of 1 to 3 showed complete remission (CR) while 100% of patients with B-content score of 4 showed CR after first induction chemotherapy.

Estimated KIR gene frequency (gf) in these AML patients was compared with 78 normal individuals recruited from Aga Khan University in Karachi (Norman et al, Gene and Immunity 2002). We found no difference in gf of KIR locus 2DL3 (0.55 vs 0.70), 3DL1 (0.75 vs 0.56), 2DL2 (0.52 vs 0.42), 2DL5 (0.42 vs 0.53), 2DS1 (0.44 vs 0.31), 2DS2 (0.42 vs 0.31),2DS5 (0.28 vs 0.28) and 3DS1 (0.28 vs 0.34) in AML cases vs normal individuals. However, we found significant difference in gene frequency of KIR2DL1 (0.42 vs 0.68) [p=0.002], 2DS4 (0.75 vs 0.47) [p=0.007] and 2DS3 (0.07 vs 0.26) [p=0.002] in AML cases compared to healthy individuals.

Conclusion: We found that the majority of patients diagnosed with AML harboring heterogenous cytogenetic abnormalities exhibit a Bx KIR haplotype with B-content score of 2. We did not find any specific cytogenetic abnormality to be associated with a particular B-content score. As we look at our data closely, it seems that it is the cytogenetic abnormality and not the B-content score that dictates the outcome after first induction chemotherapy. We found that patients with AML have decrease in gene frequency of 2DL1 (inhibitory KIR) and 2DS3 (activating KIR) while an increase in gene frequency of 2DS4 (activating KIR) compared to healthy individuals. Further studies are required to determine if variable gene frequency of these 3 KIR loci contributes towards the development of AML.

No relevant conflicts of interest to declare.