Comparison of HLA Alleles in Follicular Lymphoma and Chronic Lymphocytic Leukemia Patients Referred for Allogeneic Stem Cell Transplantation

Data recently published showed that besides the several well-known parameters, long term outcome after allogeneic stem cell transplantation (SCT) in chronic lymphocytic leukemia (CLL) may be influenced by the presence or absence of certain HLA class I alleles (HLA-A1+/A2-/B44-) (Khouri et. Al. Cancer 2011). We have also recently published an 11-year progression free survival (PFS) rate of 72% in relapsed follicular lymphoma (FL) after SCT (Khouri et al. Blood 2012). A higher relapse rate has been observed in CLL patients when compared to FL (50% vs. 4%). Since HLA subtypes played an important role in CLL, our goal in this study was to assess and compare over expressed HLA alleles in FL and CLL patients who received a SCT at our center.

Two cohorts of patients who received SCT were retrospectively studied. Group I consisted of 59 Caucasian patients (23 [39%] F: 36 [61%] M) with FL and Group II consisted of 119 Caucasian patients (27 [23%] F: 112 [77%] M) with CLL. The HLA alleles at HLA-A, -B,-C and -DRB1 loci of both groups were analyzed and the HLA typing was performed by polymerase chain reaction (PCR) amplification and oligonucleotide hybridization using commercial kits from Invitrogen (Carlsbad, Ca) or One Lambda (Canoga Park, Ca) that resulted in intermediate resolution. Patients were also typed for these loci using high-resolution methods with PCR amplification and nucleotide sequencing (Abbott, Abbott Park, Ill).

The antigen frequencies of all of the alleles of HLA-A, -B,-C AND DRB1 were calculated. Antigen frequency was defined as the percentage of the population possessing the antigen. Antigen frequency comparisons were only done for North American whites due to sample size and control group constraints. The control group was based on a sample analysis of 643 normal North American Whites. The Pearson x²goodness-of-fit test was used to validate the Hardy-Weinberg genetic equilibrium for phenotypic data. The association of various alleles with the control group was determined by using a chi-square test with Yates correction in a 2 × 2 table with 1 degree of freedom (SAS software, version 6.12, SAS Institute Inc, Cary NC). P values < 0.05 at the 95% confidence interval (95% CI) were considered significant.

A male predominance was noted in both patient groups. A total of 17 HLA-A, 29 HLA-B, 13 HLA-C and 13 HLA-DRB1 distinct alleles for FL patients and 16 HLA-A, 24 HLA-B, 13 HLA-C and 11 HLA-DRB1 distinct alleles were identified for the CLL patients. Since the predominant ethnic type in both groups were North American Whites, statistically valid comparisons of HLA antigen frequencies were only possible in this population. The observed heterozygosity for FL/CLL patients was 0.93220./0.831932 for HLA-A, 0.915254/0.949579 for HLA-B, 0.779661/0.882352 for HLA-C and 0.847457/0.941176 for HLA-DRB1. There were no untyped patients and all of the patients underwent hematopoietic stem cell transplantation.

Our analysis reveals an over expression of HLA-A*03, HLA-C*04, HLA-DRB1*01, HLA-DRB1*07 and HLA-DRB1*15 with frequencies of 25.4%, 24.1%, 22.9%, 28.8% and 8.5 % in FL patients which was significantly higher than the frequencies of 15.1% for HLA-A*03 (p value 0.005), 1.1% for HLA-C*04 (p value < .00001), 10.3% for HLA-DRB1*01 (p value <.0001), 14.4% for HLA-DRB1*07 (p value < .0001) and 15.7% for HLA-DRB1*15 (p value < .0495) in the normal population showing for the first time an over representation of these alleles in patients with FL.

In the CLL group our analysis revealed a 24.8% (p value 0.0014) frequency for HLA-A*01 which was significantly higher than the frequency of 16% (p value 0.0014) in the normal population showing an overrepresentation of this allele. The underrepresented allele was HLA-B*38 with a frequency of 3.4% compared to 12.4% (p value 0.0335) in the normal population.

When the two groups FL and CLL patients were analyzed, the significant alleles were HLA-A*01, HLA-A*03, HLA-C*04, HLA-DRB1*01 and HLA-DRB1*07.

Our results demonstrate a significant difference in HLA expression in Follicular Lymphoma and Chronic Lymphocytic Leukemia patients with the over representation of HLA-A*03, HLA-C*04, HLA-DRB1*01, HLA-DRB1*07 and HLA-DRB1*15 alleles in FL and HLA-A*01 and HLA-B*38 alleles in CLL. We do not know whether these variances account for a different graft-versus-malignancy susceptibility to donor cells between the two groups and this remains to be studied.

No relevant conflicts of interest to declare.