The effect of single and combined activating killer immunoglobulin-like receptor genotypes on cytomegalovirus infection and immunity after hematopoietic cell transplantation

Abstract

It has been shown that activating killer Ig-like receptor (aKIR) genes are important for control of cytomegalovirus (CMV) reactivation after hematopoietic cell transplantation (HCT). To date, using the broad classification of KIR haplotypes A and B, the precise role of individual KIR genes in the control of infection cannot be discerned. To address this, a consecutive case series of 211 non-T cell-depleted HCT patients all at risk for CMV were monitored biweekly for CMV DNA in plasma by quantitative polymerase chain reaction (Q-PCR) and at intervals for CMV-specific T cell immunity. Comparing patients with CMV reactivation (n = 152) to those with no reactivation (n = 59), the presence of specific aKIR haplotypes in the donor, but not in the recipient, were associated with protection from CMV reactivation and control of peak plasma CMV DNA (P < .001). A donor aKIR profile, predictive for low risk of CMV reactivation, contained either aKIR2DS2 and aKIR2DS4 or had >/=5 aKIR genes. Neither donor nor recipient inhibitory KIR (iKIR) played a role in a protective effect. CD4(+)- and CD8(+)-specific CMV immunity did not explain reduced CMV infection. The initial control of CMV infection after HCT is managed by aKIR functions, and donor aKIR haplotypes deserve further evaluation in donor selection for optimized HCT outcome.

Figure 1. Donor and recipient KIR gene frequency in HCT recipients with and without CMV reactivation

The cohort has been dichotomized according to the recipient's CMV reactivation status (■ n=152, having at least one incident of CMV reactivation; and n=59, having no CMV reactivation). The KIR gene frequency is separately portrayed for donors (Panel A) and recipients (Panel B). aKIR2DS4d represents the deletion variant of aKIR2DS4. iKIR2DL4, iKIR3DL2 and iKIR3DL3 were detected in all members of this cohort, and thus omitted from this figure. AA indicates individuals homozygous for KIR haplotype A, and BX indicates individuals either heterozygous (BA) or homozygous (BB) for KIR haplotype B. * p= 0.06, ** p≤ 0.05 using the Chi-square test.

Figure 2. CMV reactivation and aKIR profiles

Panel A: Percent CMV reactivation vs. number of donor aKIR genes: 0 donor aKIR (n=30), 1-4 donor aKIR (n=161) and equal to 5 or more aKIR, (n=20). Chi –square T test is significant for independence p=0.034. Panel B: Percent CMV reactivation vs. type of donor aKIR combinations, including No aKIR2DS2 or aKIR2DS4 (n=57), either aKIR2DS2 or aKIR2DS4 (n=118), and both aKIR2DS2 and aKIR2DS4 (n=36). Chi-square T test is significant for independence p=0.001.

Figure 3. CMV reactivation profile for each group I, II and III

Panel A: Time to first CMV positivity by Q-PCR is shown for subjects in each group (Log-Rank test p=0.004). Panel B: Time to peak Q-PCR is shown for subjects in each group (Log-Rank test p=0.015). Panel C: Amounts of CMV genome copies/ml are shown at time of first detected CMV reactivation (Kruskal-Wallis test p=0.0001). Panel D: Peak amounts of CMV genome copies/ml are shown (Kruskal-Wallis test p<0.0002).

Figure 4. Adaptive immune response in Group I, II, and III

The adaptive immune response was analyzed at days 40, 90, 120, 150, 180, and 360 post-HCT for groups I, II, and III. Panel A: Time to first 1×10⁶ CD8+/IFN-γ+ cells/L as determined by in vitro assay after stimulation with a CMV-pp65 peptide mixture or 1-2 peptides specific for HLA A*0201 and or B*07. Panel B: Time to first 1×10⁶ CD8+/IFN-γ+ cells/L as determined in vitro after stimulation with a CMV-IE1 peptide mixture or 3 peptides specific for HLA A*0201 and or *B08. Panel C: Time to first 1×10⁶ CD4+/IFN-γ+ cells/L as determined by in vitro assay after stimulation with a CMV antigen cell lysate.