Members of the Blood Products Advisory Committee to the Food and Drug Administration (FDA) convened for their 108th meeting in Rockville, Md., on Nov.1 to advise the FDA on interpretive criteria for the MP Diagnostics HTLV Blot 2.4, manufactured by MP Biomedicals LLC.
Human T-lymphotrophic virus I, or HTLV-I, has been causally associated with adult T-cell leukemia, HTLV-associated myelopathy/tropical spastic paraparesis, and HTLV-associated uveitis. HTLV-II has been associated with T-hairy cell leukemia, benign lymphocytosis, and chronic neurodegenerative disease; however, unlike HTLV-I, its causal role in disease has not been established. HTLV can be transmitted in humans by mother to child via breast-feeding; sexual transmission, particularly from infected men to their female sexual partners; illicit injection drug use (e.g., needle sharing); and contaminated blood transfusions.
Overview of product submitted for licensure review
FDA recommended screening of whole blood donors for antibodies to HTLV-I in 1988, and added screening for antibodies to HTLV-II in 1997. 21 CFR 610.40(a) specifically lists HTLV-I and II as required tests for donors of whole blood. Current testing methodologies include two FDA-licensed screening assays for antibodies to HTLV-I/II — one enzyme immunoassay (EIA) and one chemiluminescent assay — that do not distinguish between HTLV-I and HTLV-II. There is not, and has not been, an FDA-licensed supplemental (additional, more specific) test for specimens repeatedly reactive on the screening assays. Consequently, there is no algorithm for reentry of deferred donors. Donations with repeatedly reactive (RR) results are not used for transfusion and donors are indefinitely deferred whenever they are RR on more than one donation or when a second assay of a different type is RR on the same donation.
Blood donor centers have used whatever methods are available to enhance donor counseling messages. Non-FDA-approved tests are allowed to be used for purposes of donor counseling. Some establishments have used additional testing developed by the California Department of Public Health Laboratory (CDPHL). The CDPHL algorithm consists of a series of laboratory developed tests (LDTs) run in a defined sequence with the overall interpretation determined by the results of all tests performed. Consequently, donor counseling messages across the United States are inconsistent and donors are encouraged to take results to their personal physicians.
Highlights from the MP Diagnostics HTLV Blot 2.4 performance studies contained in the Issue Summary prepared by the FDA for the BPAC were reviewed. FDA also noted studies in which they stated that western blot indeterminate specimens due to p19 plus p24 bands may represent HTLV infection.
The MP Diagnostics HTLV Blot 2.4, marketed by MP Biomedicals Asia Pacific, has been available in over 26 countries as a supplemental HTLV assay since 1995. In 2004, the assay was CE marked.1 The blot makes use of truncated recombinant proteins and peptides developed to decrease cross-reactivity and assist with differentiation between HTLV-I and HTLV-II. Version 2.4 uses a combination of three recombinant envelope (env) proteins — truncated p21e, referred to as GD21; and two peptides, one associated with HTLV-I, and the other with HTLV-II. Version 2.4 relies on viral lysate for reactivity to the core or gag gene. In the version 2.4 interpretation criteria donor samples exhibiting HTLV-gag indeterminate patterns/profiles (HGIP) are seronegative.
The assay remains in use in the U.S. under an open IND (investigational new drug application) while the assay is under review by FDA.
California Department of Public Health Laboratory
LDTs have been a major component of the algorithm developed by the CDPHL. The following are tests and date of development/implementation:
- 1983 - IFA - Immunofluorescence assay
- 1986 - WB - Western blot
- 1987 - RIPA - Radioimmunoprecipitation assay
- 1988 - PCR - Polymerase chain reaction
In addition to the LDTs, various commercial EIAs and WBs have been employed in the CDPHL algorithm. In 1997, the laboratory was first contacted by blood centers requesting confirmatory testing for repeatedly reactive samples. Additional customers requested the service in 2001.
The algorithm in use since 1997 consists of screening all samples by EIA and IFA simultaneously. Concordant samples are reported; positives are typed by IFA. Discordant samples are reflexed to WB and RIPA if needed. The lab does not score intensity of bands on the WB. All bands are recorded as positive or negative. If two test results agree, the result is reported as an overall interpretation, either antibody 'detected' or 'not detected'. Samples having an EIA reactive, IFA nonreactive and WB positive results are further tested by RIPA. The overall interpretation is antibody detected (not typed) when the RIPA is positive and inconclusive when the RIPA is negative. When no two test results agree, the result is reported as inconclusive.
Results provided by the CDPHL are widely used in donor counseling but cannot be used to reenter donors to the available pool for blood donation.
Experience of U.S. Blood Centers with HTLV blood donation screening
The American Red Cross (ARC) like most blood centers has used a variety of assays since 1988 for screening blood donors for HTLV-I and then HTLV-II, and like other blood centers has deferred and counseled donors without offering an algorithm for reentry. In-date components from RR donors are retrieved. Lookback is not required although ARC did perform lookback steps until 2008, due to no yield. ARC prevalence/incidence data support that these rates are low and decreasing and that lookback has no value (Notari et al. 2012 AABB Annual Meeting). It is estimated that more than 100,000 donors have been deferred since the start of HTLV testing with no risk other than HTLV RR results. Many of the donors have been counseled using CDPHL results, but cannot be offered reentry without a licensed supplemental/confirmatory test.
ARC has worked with MP Biomedicals to provide data on U.S. blood donors and continues with a follow-up study under an open IND that makes use of a dual EIA algorithm. All donor notification and counseling uses interpretations found in the MP Diagnostics HTLV Blot 2.4 package insert (including interpretation of negative in the presence of single or combinations of gag protein bands in the absence of p24/env). Donors have the option to opt out of the follow-up study. The purpose of the study is to demonstrate that HGIP samples do not evolve to seropositives — e.g., are not related to HTLV infection.
The Creative Testing Solutions (CTS) experience has been similar to ARC. A variety of assays have been used in the dual EIA algorithm. Donor counseling messages have been supplemented by results from the CDPLH and more recently from results obtained from an open IND with the Innogenetics InnoLIA HTLV-I/II WB. CTS reported on results from non-U.S. donors as well as US donors. Among U.S. blood donors, gag-only patterns on HTLV-I/II lysate WBs represent non-specific reactivity unrelated to HTLV-I or HTLV-II infections.
Just as with the MP Biomedical WB, the HTLV InnoLIA CE-marked package insert interprets gag-only profiles as negative. These criteria continue to be used by CTS in the open IND under which they are working.
Ownership of the InnoLIA WB has changed and it is not clear that the product is intended for the U.S. market.
Open Public Hearing
AABB, ARC and America's Blood Centers presented a joint statement encouraging the BPAC to support the interpretive criteria of the MP Diagnostics HTLV Blot 2.4 as it has been used in Europe, Asia, and other countries since 1995, recognizing that the interpretive criteria must carry forward to donor counseling messages.
"Since 1988, we conservatively estimate that greater than 200,000 donors testing falsely-positive on licensed HTLV screens, in the absence of other evidence of infection, have been deferred. Some of these donors have had additional testing performed for counseling purposes, but many have not. Thus, these donors enter the health care system with incomplete data leaving primary care physicians confused as to the meaning of a reactive screening test (and the meaning of additional research supplemental tests). Additionally, since 1988, no donor deferred for HTLV false reactivity has been eligible for reentry. That is, many healthy donors with HTLV false positivity remain unable to donate.
The three organizations encourage FDA licensure of the MP Biomedicals, version 2.4 WB as an HTLV confirmatory test to be used for donor counseling and from which to develop a donor re-entry algorithm. Licensure allows better oversight of production, less reliance on complex algorithms, more assurance of a continued supply chain, improved turn-around times, and gives manufacturers the message that developing a confirmatory test for the U.S. market is a worthwhile endeavor. With licensure, we need to ensure appropriate messaging to donors that avoids unnecessary donor anxiety from clinically irrelevant indeterminate interpretations of nonspecific gag (non-env) banding. The scientific data argue persuasively that such test results should be interpreted as negative. As part of confirmatory testing algorithms, we strongly encourage the FDA to allow the industry to continue to use the dual screening test algorithm that has served us well for nearly 20 years and to retain the ability for donors to remain eligible for donation until reactive by two licensed screening tests on the same donation or a single screening test on two donations. The use of a dual test algorithm with orthogonal screening assays minimizes the number of WBs that need to be performed, and most importantly, provides a necessary opportunity to reduce the number of donors with biological false reactivity that is associated with triggering confirmatory testing from a single manufacturer's reactive screening test. Screening tests validated extensively for sensitivity allow false positives — i.e., those discordant on the two screening tests — to avoid further testing, and will serve in data collection for the validation of a donor reentry algorithm."
The BPAC committee spent some time discussing the importance of data from non-U.S. blood donors, the populations with high rates of HTLV infections, and the value of available PCR tests. Questions posed to the committee and resulting votes are listed below. The questions were rewritten after original publication in the "Federal Register."
Q1. For blood donors with repeatedly reactive results on an HTLV antibody screening test, are the data sufficient to conclude that individuals with the following bands on the MP Diagnostics HTLV Blot 2.4 are unlikely to be infected with HTLV-I or HTLV-II?
- Single gag band (e.g., p24 only) Vote: 14 Yes, 1 No. The nonvoting industry rep indicated Yes
- Multiple gag bands (e.g., HGIP) Vote: 14 Yes, 1 No. The nonvoting industry rep indicated Yes
Q2. For blood donors with repeatedly reactive results on an HTLV antibody screening test, are the data sufficient to conclude that individuals with the following bands on the MP Diagnostics HTLV Blot 2.4 are not infected with HTLV-I or HTLV-II, allowing results to be considered negative?
- Single gag band (e.g., p24 only) Vote: 6 Yes, 7 No, Abstain 2. The nonvoting industry rep indicated Yes
- Multiple gag bands (e.g., HGIP) Vote: 10 Yes, 3 No, Abstain 2. The nonvoting industry rep indicated Yes
Q3. If the data are insufficient to conclude that blood donors with a single gag band or multiple gag bands without p24 are not infected with HTLV-I or HTLV-II, please comment on any additional studies that should be performed.
There is an open IND with the MP Biomedicals product. See Experience of U.S. Blood Centers with HTLV blood donation screening. Discussion of question 3 concerned inclusion of PCR in the donor follow-up algorithm to attempt to gather this data.
- According to the European Commission, CE marking indicates the product is assessed before being placed on the market and meets European Union safety, health, and environmental protection requirements. http://ec.europa.eu/enterprise/policies/single-market-goods/cemarking/index_en.htm.