Cytomegalovirus (CMV) Pentameric Complex (PC) Neutralizing Antibodies (nAb) from a Randomized, Controlled Trial of CMV-Specific Intravenous Immunoglobulin (IVIG) for the Prevention of Primary CMV Infection after Hematopoietic Cell Transplantation (HCT)

Abstract

Prevention of CMV disease after HCT remains a challenge. In addition to antivirals, immune-based strategies such as active and passive immunization may have potential roles preventing infection. CMV entry into epithelial and endothelial cells requires distinct viral proteins including UL128, UL130, UL131A, gB and gH/gL that combine to form a PC. A nAb assay was developed by Gerna et al. that measures nAb activity against PC, although its clinical application in HCT patients has not been described. In 1991, Bowden et al. conducted a study where CMV IVIG was administered as prophylaxis to D+/R- patients early after allogenic HCT. Although it showed reduced CMV infection in CMV IVIG recipients, CMV disease was not reduced thus its use was never adopted. This impact on infection suggests the possibility that CMV IVIG inhibits infection via neutralization of an unidentified entry pathway that may include PC. From the original cohort, we tested 538 serum samples from 61 patients using CMV DNA polymerase chain reaction (PCR) to compare clinically significant viral load (≥ 4 log10 IU/ml) or histopathologically detected CMV between groups. We also used a CMV nAb assay to evaluate anti-PC neutralizing capacity. The assay uses retinal pigmented epithelial (ARPE-19) cells exposed to serial dilutions of serum combined with a laboratory CMV strain, BADrUL131-Y4, that contains a green fluorescent protein (GFP) cassette. After one hour incubation, cells are washed and incubated for one week. Fluorescence is measured and we construct curves that plot viral neutralization against serum dilution and from these we extrapolate an IC-50; that is the dilution where 50% virus neutralization is achieved. After excluding three patients infected prior to day 21 post-transplant, there were 27 CMV IVIG and 31 control patients. Neither cumulative incidence of CMV infection (Figure 1, p=0.55), nor IC-50 values (Figure 2, p=0.19) differed by study arm, though observed median IC-50 values were higher in the CMV IVIG arm (5.8) than in the control arm (4.8). We found no association between IC-50 and risk of CMV infection (HR=1.8, 95% CI 0.6-5.3, p=0.31). Using modern CMV detection methods, our study suggests CMV IVIG does not result in decreased CMV viral load. Although the PC nAb composition of the CMV IVIG used is unknown, it did not appear protective against CMV infection. We successfully evaluated CMV PC entry-specific neutralizing activity in the HCT setting using a nAb assay, however evaluation among larger cohorts is needed to determine its clinical utility.