CBF

Also see: Annotated Bibliography, II. TRANSPLANTATION OF ADULTS USING CORD BLOOD UNITS

  1. Reexposure of cord blood to non-inherited maternal HLA antigens improves transplant outcome in hematologic malignancies. van Rood JJ, Stevens CE, Smits J, Carrier C, Caarpenter C, Scaradavou A. Proc Natl Acad Sci USA. 2009;106:19952-7

Cord blood (CB) hematopoietic stem cell transplantation can be successful even if donor and recipient are not fully matched for human leukocyte antigens (HLA). This may result from tolerance-inducing events during pregnancy but to date this concept has not been tested in CB transplantation. The authors explored the question as to whether in utero exposure to noninherited maternal antigens (NIMA), as a result of two-way traffic of cells and molecules such as soluble HLA antigens between mother and fetus during pregnancy and consequent development of immunity and tolerance, may affect graft responses to recipient HLA. They suggested that CB grafts with a NIMA match to the patient’s mismatched antigen might have improved outcomes and, therefore, might guide us in selecting mismatched donors.

The authors analyzed the outcomes of the 1,121 patients transplanted with a single CB for hematological malignancies, including myelodysplasia (MDS). Among 1,059 patients with mismatched grafts, 79 (7%) received a mismatched unit that had a NIMA that was identical to a mismatched antigen of the recipient. The latter are referred to as ‘‘NIMA matched transplants’’ (NMTs). The remaining 980 mismatched grafts had no NIMA match and are referred to as “no NIMA match transplants” (no-NMTs). Of these patients, 79 patients had a mismatched antigen that was identical to a donor NIMA, 25 with one HLA mismatch (MM), and 54 with two.

If there was a NIMA match, transplant-related mortality (TRM) was improved, especially in patients >10 years (P = 0.012) as were overall mortality and treatment failure (P = 0.022 and 0.020, respectively, in the older subset), perhaps related to improved neutrophil recovery, especially in patients who received a low total nucleated cell (TNC) dose (P = 0.031). Posttransplant relapse rate also tended to be reduced, especially in patients with myelogenous malignancies given units with a single HLA mismatch (P = 0.074). The incidence of severe aGVHD and cGVHD was similar to rates reported in other series but was not significantly associated with matching for NIMA.

These findings represent unique evidence that donor exposure to NIMA can improve survival in unrelated CB transplantation and might reduce relapse. While these data need to be confirmed, it might be appropriate to select HLA mismatched CB grafts with a NIMA match preferentially for their antileukemic effect.

A very significant aspect of the current work is that, by matching for donor NIMAs in search algorithms of CB inventories, the probability of selecting a graft with an optimal outcome will increase significantly. For a unit and mother with six identified antigens at these three loci, a single substitution produces 6 new virtual phenotypes, increasing the number of optimal units sixfold. Allowing for two NIMA substitutions for grafts with two HLA mismatches would increase these units by up to 18-fiold. A 6-fold increase in the probability of finding an optimal unit, for example, would be equivalent to expanding the effective current world inventory to over 2 million units.

[Note: This work was presented at the American Society of Hematology Annual Meeting, December 4-8, 2009 --- see Abstract 661.

  1. The 6th Annual International Umbilical Cord Blood Transplantation Symposium which was held in Los Angeles, June 6-7, 2008. A CD containing the audio and slides presented at the Symposium is now available. For a free copy send your postal mailing address to: symposiumCD@cordbloodforum.org.

A Featured Presentation from the 2008 International Umbilical Cord Blood Transplantation Symposium:
[One of a number of important points made in this presentation regarding the outcomes of 991 patients is that results are improved significantly using CB units that are 6/6 HLA matches compared to units with any degree of mismatching. This important finding emphasizes the fact that efforts should be made to greatly increase the world wide inventory of cord blood units.

Dr. Barker’s presentation can be reviewed in its entirety on the Symposium CD.]

An Analysis of the Impact of Cell Dose & HLA-Match on the Survival of 991 Patients Transplanted with Single Units for Hematologic Malignancy. J. N. Barker, A. Scaradavou, C.E. Stevens, P. Rubinstein.

Dr. Barker pointed out that TNC dose and HLA-match are both determinants of TRM & DFS after UCB transplantation (UCBT). She analyzed the impact of pre-freeze TNC dose and HLA-match upon the 3 year transplant outcomes in recipients of single unit ablative UCBT.
The cell doses expressed as cryopreserved TNC x 107/kg were 0.7-2.4 (23% of transplants), 2.5-4.9 (38%) 5.0-9.9 (26%) and ≥10 (13%). HLA matches (HLA-A and -B at antigen level and DRB1 at allele level) were 6/6 (5% of transplants), 5/6 (33%), 4/6 (56% and 3/6 (6%). Diagnoses were ALL (45%), AML (32%), CML (12%), other leukemias (4%) and MDS (7%). The median age was 9.2 years with a range of 1 month to 62 years.

Results indicated that when using CB units with zero HLA mismatches, TRM was significantly reduced (p= 0.003) and DFS was significantly increased (p=005). Further, 6/6 matched units were associated with significantly lower grade III-IV acute GVHD (p=0.025). The data indicated that it is preferable to select a CB unit with zero HLA mismatches over larger mismatched units (although the cell dose threshold has not been determined).

Further results indicated a higher TNC dose was associated with faster engraftment and a higher percentage of engraftment, and that the number of HLA mismatches was not associated with relapse risk.

Proposed unit selection priorities based on these results were;
1st choice: 0 mismatches (MM) with any TNC dose (although the dose threshold has not been determined)
2nd choice: 1 MM with TNC >2.5/kg.
3rd choice: 2 MM with TNC >5.0/kg.
To be avoided are (1) units with 3 MM, (2) units with 2 MM and TNC 2.5-4.9/kg, (3) units with 1 or 2 MM with cell dose <2.5/kg

An important problem is that most adults and teens don’t have any “good” single units. Accordingly, the authors indicated the obvious: there is a need for an increased inventory of cord blood units.

  1. Donor selection for unrelated cord blood transplants. Gluckman E, Rocha V. Curr Opin Immunol. 2006; 18:565-70.

OVERVIEW

Hematopoietic stem cell transplantation (HSCT) from an unrelated cord blood (UCB) is now standard practice for the treatment of hematological disorders. The number of unrelated cord blood transplants is increasing, with more than 8000 patients reported worldwide.

Umbilical cord blood transplantation (UCBT) has extended the availability of allogeneic HSCT to patients who would otherwise not be eligible for this curative approach. The number of UCBTs has increased dramatically, because several studies have demonstrated that results from HLA- mismatched UCBTs were comparable to those from HLA- matched unrelated bone marrow transplants in children and in adults.

In comparison with other sources of HSCT, UCB offers logistic and clinical advantages, such as: faster availability of banked cryopreserved UCB units; extension of the donor pool owing to tolerance of 1-2 HLA mismatches; lower incidence and severity of acute GVHD; lower risk of transmitting infections by latent viruses; lack of donor attrition; lack of risk to the donor; and higher frequency of rare haplotypes.

One of the major complications of UCBT is delayed engraftment owing to the low number of cells infused, which is 10-times less than a BM collection. Study of the role of cell dose and HLA compatibility to guide transplant centers in the selection of the best unit for transplant is extremely important.

IMPACT OF CELL DOSE AND HLA MATCHING ON OUTCOMES

The Eurocord group has recently analyzed the impact of diagnosis, cell dose and HLA incompatibilities in patients receiving a single UCBT in 925 patients with malignant disease and 279 patients with non-malignant disease. Donor-recipient histocompatibility was determined by serology or antigen typing for HLA- and HLA-B and by DNA typing for HLA-DRB1.

Patients with malignant diseases. The median number of nucleated cells (NCs) infused was 3.1 x 107 NC/kg (range 2-5 x 107 NC/kg). At day 100, the cumulative incidence (CI) of neutrophil recovery was 77.4% and of platelet recovery to 20,000/µl was 54.7%. Engraftment was associated with the number of cells infused (p<0.0001). HLA was a second factor, with a difference between 0-1 (81%), 2 (75%) and 3-4 (63%) HLA incompatibilities (p=0.037). There was no correlation between engraftment and the type of HLA mismatches (class I or class II, or HLA-A, -B or –DRB1).

The CI of aGVHD grade II-IV was 33% and the CI of aGVHD grade III-IV was 17.3%; it was not associated with the number of cells infused or with the number of HLA disparities. The CI of cGVHD was 28.6% and it was increased in the group who received a low cell count or a 3-4 HLA-mismatched transplant.

The CI of relapse was 23.1% at 100 months and it was not associated with the number of cells infused, whereas increasing the number of HLA disparities decreased the relapse incidence.

The CI of overall survival (OS) and disease-free survival (DFS) at 100 months was 33.4% and 30.8%, respectively. Patients who received <3 x 107 NC/kg at freezing of cord blood unit or ≤2.1 x 107 NC/kg at thawing had decreased probability of survival The number of HLA incompatibilities had no influence on OS or DFS. This was explained by the positive impact of the number of HLA mismatches on relapse and the negative impact on engraftment.

In summary for patients with malignant diseases: Cell dose was the most important factor for outcome; a minimum cell dose of 3 x 107 NC/kg at collection and of 2 x 107 NC/kg at infusion must be targeted. The number of HLA mismatches increased the risk of delayed engraftment and led to a higher incidence of TRM and cGVHD; however, it decreased the risk of relapse, resulting in an absence of the role of HLA mismatches for OS and DFS. The type of HLA mismatch did not influence outcomes, but matching for HLA-DRB1 seems better for patients receiving a graft that has two HLA incompatibilities. Increasing cell dose abrogated the effect of HLA mismatches, but not for grafts with 3 or 4 HLA incompatibilities.

Patients with non-malignant diseases. The median number of NCs infused was 6.4 x 107 NC/kg (range 0.8-66 x 107NC/kg). At day 100, the CI of neutrophil recovery was 69.3% and CI of platelet recovery was 50%. Both neutrophil and platelet recoveries were associated with the median number of cells infused (p<0.000055). HLA was also an important factor associated with neutrophil recovery, with a statistical difference between 0-1 and ≥2 HLA mismatches (p=0.046). The role of HLA mismatches was abrogated by increasing cell dose, except in the group of patients who received a 3-4 HLA-mismatched transplant. There was no correlation between neutrophil recovery and the class of HLA mismatches (class I or class II, or HLA-A, -B or –DRB1).

The CI of aGVHD grade II-IV was 31.8% and grade III-IV 18%, and was only associated with the number of HLA incompatibilities (p=0.0029). The CI of cGVHD was 24% and was also associated with the number of HLA incompatibilities (p=0.01).

The CI of OS at 100 months was 49% and it was influenced by cell dose and by the number of HLA mismatches. The group who received an UCBT with <3.5 x 107 NC/kg at infusion and a 2-3 HLA-mismatched transplant had <20% survival. Increasing cell dose partially abrogated the effect of HLA mismatches.

In summary for patients with malignant diseases: Patients with non-malignant diseases must receive a higher cell dose to obtain engraftment than patients with malignant disorders; it should not be below 4.9 x 107 NC/kg at collection and 3.5 x 107 NC/kg at infusion. In non-malignant disease, HLA mismatches played a major role for engraftment, GVH and survival; it is partially abrogated by increasing cell dose, and two HLA-DRB1 mismatches seemed to have an adverse effect.

OTHER FACTORS

The role of CD34+ cells: Several authors have shown that the number of CD34+ cells in the transplant correlated with engraftment. Unfortunately, this measurement cannot be used for comparative studies between centers because of the absence of standardization of the counting method.

Colony forming units (CFU-GM) is another method for counting the stem cell content. However, there is too much inter-laboratory variability.

Role of allelic typing in UCBT outcomes. An analysis of 122 patient-CB donor combinations using high-resolution (HR) typing for both HLA class I and class II loci showed no statistical association between the number of HLA mismatches and neutrophil recovery; however, based on HLA HR typing in the rejection direction (donor alleles not shared by the recipient), 1 or 2 HLA-A HR disparities were associated with reduced incidence of engraftment (p=0.04). An analysis of the influence of single alleles on the subtyping level in GVHD direction only for the HLA-B (comparing 0 mismatches versus 1 and 2 locus mismatches), indicated that incompatibilities in the HLA-B locus were associated with the incidence of a GVHD grade II-IV (p=0.04). In this study, there was no benefit of additional HR typing for HLA-A, -B, -C, -DR and –DQ for outcomes after UCBT.

Current recommendations for choosing the bests CB unit. In order of preference: 6/6 matched CB and >3 x 107NC/kg; 5/6 matched CB and >4 x 107 NC/kg; 4/6 matched CB and >5 x 107 NC/kg. Use of units with <3 x 107 NC/kg and/or 3-4 HLA mismatches is not recommended; in this case a double CBT might be considered. (See Annotated Bibliography, Category III, Multi-Cord Transplants)

  1. Principles and tools for selection of umbilical cord blood and unrelated adult donor grafts. Lee SJ, Kamani N, Confer D. Biol Blood and Marrow Transplant 2008;14(Suppl 1):112-119.

The impact of HLA matching on major outcomes in UCB transplantation continues to be refined. TNC was previously thought to be the sole determinant of outcome with partially HLA matched UCB transplantation, but HLA matching, particularly at low TNC dose, appears to play an important role. Relatively small sample sizes limit the consistency of findings from cord blood studies, but the consensus supports consideration of both TNC and HLA matching in the selection of optimal UCB units.

UCB graft cell dose is a critical determinant of hematopoietic recovery and survival after UCBT, but there is increasing evidence that HLA match is also a key factor in outcome. Current data suggest that HLA match is critically important in the setting of a low cell dose. The complete elucidation of the impact of graft dose and match on UCBT outcome will require the analysis of larger cohorts of patients.

The impact of a 1 versus 2 antigen mismatch, the “trade-off” between HLA-match and cell dose in unit selection, the importance of allele-level matching at HLA-A and B, the match vector, and whether HLA-C or DQB1 should be considered in the selection of UCB units for transplantation cannot be fully discerned at the current time.

Currently, the NMDP recommends typing all loci (A, B, C, DRB1 and DQB) at the allele level. Matching should follow the current standard of intermediate level for HLA-A and -B, and allele level for HLA-DRB1. All recommendations are based on selection of a unit with an appropriate cell dose. Currently available data would consider this to be a unit that has >2.5-3.0 x 107 TNC/kg recipient body weight.

Tools for locating the optimal adult donor or UCBA UNIT: NMDP provides software to transplant centers (TRANS Link®) that allows real-time searching of the complete NMDP inventory of adult donors and UCB units. TRANS Link produces a donor/UCB list that is sorted with the best of potential donors/UCB at the top. An NMDP innovation named HapLogicsm predicts the likelihood of allele-level matching based on calculated HLA haplotype frequencies within major racial and ethnic populations. Another NMDP software product is the Multi-Cord Tool which evaluates HLA matching between the proposed recipient and the UCB units as well as matching between UCB units. The tool was developed to simplify the UCB selection process for double cord transplantation.

[For more details, also see the editorial by Kamani et al (Annotated Bibliography, V. HLA matching, citation #5 below]
  1. State of the art review: HLA matching and outcome of unrelated donor umbilical cord blood transplants. (Editorial) Kamani N, Spellman S, Hurley CK, Barker J, Smith FO, Oudshoorn M, et al Biol Blood and Marrow Transplant 2008;14:1-6.

This editorial summarizes current data and provides guidance in selecting UCB units for unrelated donor UCBT based on HLA matching. Of note is the fact that much of the data on the impact of HLA match on UCBT is currently preliminary or inconclusive so that guidelines will be refined over time. Also to be noted is that studies by various investigators often result in conflicting conclusions.

When reviewing the CB transplant literature, it is important to note that the majority of UCBTs reported have utilized matching at the antigen level for HLA-A and HLA-B loci and at the allele level for HLA-DRB1 loci.

Impact of HLA matching on engraftment after UCBT. In the largest analysis done to date on 562 UCBT recipients, Rubinstein et al have shown that there is a progressive delay in myeloid engraftment by day 42 with increasing HLA mismatching. However, the authors could not detect a significant difference between those who received grafts mismatched at 1 or 2 antigens.

A study by Eapen et al compared outcomes of 503 UCBTs and 282 UBMTs in children <16 years with acute leukemia to assess the influence of both cell dose and HLA matching on outcome. These authors found that higher cell doses resulted in a higher probability of both neutrophil and platelet recovery in 1 antigen-mismatched UCBT but had no effect in 2-antigen mismatched transplants, suggesting that cell dose may not be able to overcome the adverse impact of mismatching in the setting of 4 out of 6 matched UCBT. However, an EBMT study was unable to demonstrate a statistically significant interaction between the cell dose and HLA disparities for either neutrophil or platelet recovery.

In summary, whereas cell dose is important for engraftment in UCBT, HLA match also appears to impact the engraftment rates.

Impact of HLA matching on GVHD. A Eurocord study showed that whereas the degree of matching did not impact overall GVHD risk, the risk of grade III-IV GVHD was higher in recipients of UCB where class I and II disparities coexisted between donor and recipient. A COBLT study indicated that HLA matching impacted grade II-IV risk with a significantly higher risk of aGVHD in recipients of 4/6 matched UCB compared to 5-6/6 matched UCB. A study by Eapen et al failed to show a correlation between HLA match and aGVHD or cGVHD risk among recipients of UCB transplants.

Role of HLA compatibility on survival after UCBT. Only a few reports of UCBT have analyzed the effects of HLA mismatching on patient survival. Studies by Rubinstein et al and Wagner et al indicated an association of HLA-mismatching with the outcome of UCBT. In contrast, a study of 550 UCBTs by Eurocord failed to find an effect of HLA disparity on 3-year survival. In the Eurocord analysis of patients with malignant diseases, increasing HLA disparity resulted in lower rates of engraftment and higher treatment-related mortality and cGVHD, but this did not translate into a lower disease-free survival or overall survival because of a lower relapse rate. HLA disparity did impact survival for patients with nonmalignant diseases.

High-resolution HLA matching. The impact of high-resolution HLA matching in UCBT has been investigated in a number of papers. Studies by Ohnuma et al and Cornetta et al suggested that high-resolution HLA typing may help select UCB units better suitable for a favorable outcome. However, Kogler et al retrospectively typed 122 UCBT donor and recipient pairs by high resolution at HLA-A, -B, -C, -DRB1, and –DQB1 and failed to show any association with survival in univariate analysis.

Summary. Although UCB graft cell dose is a critical determinant of hematopoietic recovery and survival after UCBT, there is increasing evidence that HLA match is also a key factor in UCBT outcome with mismatch adversely impacting on both engraftment and survival. It is not currently known how cell dose and HLA match interact and it is not clear whether the same criteria will apply to both pediatric and adult recipients.

All recommendations are based on selection of a unit with an appropriate cell dose. Currently available data would consider this to be a unit that has >2.5-3.0 x 107 total precryopreserved nucleated cells per kg recipient body weight. The interaction between cell dose and HLA matching is especially critical in adults undergoing UCBT and underlines the need for drastic increases in the unrelated cord blood inventory.

  1. Hematopoietic stem-cell transplants using umbilical-cord blood. Gluckman E. N Engl J Med 2001; 344:1860-1861. Extract

Eurocord data indicate that recipients of <1 X 107 nucleated cells/kg had a transplant related mortality of 75%, whereas patients infused with at least 3 X 107 nucleated cells/kg had a transplant related mortality of only 30%.