16th IHIW: international histocompatibility working group in hematopoietic cell transplantation

The International Histocompatibility Working Group is a collaborative international effort to understand the HLA and non-HLA genetics of the transplantation barrier. The Working Group is comprised of experts in the fields of histocompatibility and immunogenetics, hematopoietic cell transplantation and outcomes research. Data for 25 855 unrelated donor transplants were submitted in support of research studies for the 16th International Histocompatibility Workshop. Active investigation is in progress in seven key areas: the impact of HLA matching, role of race and ethnicity, identification of permissible HLA mismatches, haplotype-associated determinants, minor histocompatibility antigens, immune response genes and KIR genetics. New hypotheses for the 16th workshop were developed for immunogenetic studies in cord blood and haploidentical-related donor transplantation.

Epistasis between the MHC and the RCA alpha block in primary Sjögren syndrome

OBJECTIVE

The RCA alpha block (Regulators of Complement Activation, 1q32) contains critical complement regulatory genes such as CR1 and MCP. This study examined RCA alpha block haplotype associations with both disease susceptibility and diversification of the anti-Ro/La autoantibody response in primary Sjögren syndrome (pSS).

METHODS

115 patients with pSS and 98 controls were included in the study. 93 of 109 (85%) of the patients with pSS were seropositive for Ro/La autoantibodies. The Genomic Matching Technique (GMT) was used to define RCA alpha block ancestral haplotypes (AH).

RESULTS

RCA alpha block haplotypes, AH1 and AH3, were both associated with autoantibody-positive pSS (p = 0.0003). Autoantibody associations with both HLA DR3 and DR15 have been previously defined. There was an epistatic interaction (p = 0.023) between RCA alpha AH1 and HLA DR3, and this genotypic combination was present in 48% of autoantibody-positive patients with pSS compared with 8% of controls. This epistasis is most simply attributable to an interaction between C4 and its receptor, CR1, encoded within the RCA alpha block. Both DR3 and a relative C4 deficiency are carried on the major histocompatibility complex 8.1 ancestral haplotype. Only four of 92 (4%) autoantibody-positive patients with pSS did not carry any risk RCA alpha or HLA haplotype, compared with 36 of 96 (38%) controls, and there were differences in haplotype frequencies within autoantibody subsets of pSS.

CONCLUSIONS

Normal population variation in the RCA alpha block, in addition to the major histocompatibility complex, contributes genetic susceptibility to systemic autoimmune disease and the autoantibody response. This finding provides evidence for the role of regulation of complement activation in disease pathogenesis.

14thInternational HLA and Immunogenetics Workshop: report on hematopoietic cell transplantation

Deciphering the role of human leukocyte antigen (HLA), killer immunoglobulin like receptor, and immune response genes in a model as complex as unrelated donor hematopoietic cell transplantation is a challenge. The allelic diversity of these genes is shaped by the race and ethnicity of transplant donors and recipients. Coupled with the genetic polymorphism is the complexity of clinical phenotypes of transplant populations: donor and recipient demographic characteristics and the regimens used by transplant physicians to prepare patients for transplantation and to prevent and treat graft-vs-host disease (GVHD). Furthermore, GVHD is itself a complex disease shaped by both genes and 'environment'. How does one begin to deconstruct the genetic barrier to understand risk factors important to transplant outcome? To begin with, population-based studies, particularly retrospective ones, benefit from adequate sample sizes to measure genetic effects. The more homogeneous the population for variables that influence clinical endpoints, the higher the likelihood that a real genetic effect can be uncovered. Even so, the feasibility of studies can be hampered if genotype and clinical data are not both complete and precise. For studies of HLA, diversity of alleles and antigens contributed by ethnically different transplant populations is an asset, because not only can a broader range of HLA mismatches be studied but they provide the opportunity for side-by-side analyses that may yield clues as to why transplant outcomes differ between populations.

The common marmoset as a novel preclinical transplant model: identification of new MHC class II DRB alleles and prediction ofin vitroalloreactivity

The difficulties with using nonhuman primate species such as rhesus macaques and baboons have led us to investigate the common marmoset (Callithrix jacchus) as an alternative preclinical model for transplantation research. This requires reliable methods of detecting alloreactivity between donor and recipient pairs, particularly if colonies are inbred and share just a few common alleles for leucocyte antigens. We firstly identified marmoset major histocompatibility complex (MHC) Class II DRB genes (Caja-DRB*W1201, Caja-DRB1*03, Caja-DRB*W16) using sequence-based typing techniques. Genomic DNA (n= 49) was extracted from whole blood or spleen tissue. Exon 2 of target genes was amplified by PCR using primers specific for known marmoset alleles, and then sequenced using ABI PRISM((R)) Big Dye Terminator technology and Assign sequence analysis software. DRB*W1201 was universally present. Eight DRB*W16 alleles and five DRB1*03 alleles were identified in this colony. We also identified two previously unreported DRB*W16 alleles, and confirmed inheritance of these alleles within several sibling groups. Subsequently, we investigated whether matching at MHC Class II DRB loci alone could predict alloreactivity, as assessed in vitro by two-way mixed lymphocyte reactions (MLRs). Fully DRB-matched, partially mismatched and fully mismatched animal pairs were prospectively chosen. MLR was performed using mononuclear cells (MNC) isolated from whole blood by density gradient separation. T-cell proliferation after 5-day culture was measured by (3)H-thymidine incorporation. Combined MNC from fully mismatched and partially mismatched animal pairs exhibited significant in vitro T-cell proliferation above single cell controls (P < 0.01). MNC from fully DRB-matched (but unrelated) animal pairs exhibited no proliferation compared with controls (P= 0.3). Using DRB genotyping, suitably alloreactive donor-recipient pairs may therefore be rapidly and accurately identified for use in further studies of cellular and solid organ transplantation.

Donor methylenetetrahydrofolate reductase genotype is associated with graft-versus-host disease in hematopoietic stem cell transplant patients treated with methotrexate

Methotrexate (MTX), used as a graft-versus-host disease (GvHD) prophylactic agent in hematopoietic stem cell transplantation (HSCT), exerts its effect via folate cycle inhibition. A critical enzyme involved in folate metabolism is 5,10-methylenetetrahydrofolate reductase (MTHFR). We examined the association of a single nucleotide polymorphism (SNP) at position 677 in the MTHFR gene on GvHD outcomes in allogeneic HSCT patients administered MTX. MTHFR genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) on 193 HSCT patients and donors. A total of 140 patients were transplanted with an HLA-matched related donor and 53 with an unrelated donor. GvHD outcomes were compared between genotypes by univariate and multivariate analysis. The combined donor 677CT and TT genotypes were associated with a decreased incidence of GvHD (acute and chronic combined) in HSCT recipients with an HLA-matched related donor (75% at 1 year in the CT and TT group compared with 91% in the wild type CC group, P=0.01), increased time to onset of first GvHD (P=0.001) and time to first GvHD treated with systemic therapy (P=0.022). Unrelated donor MTHFR genotype was not associated with outcome parameters and no associations of recipient genotype in either related or unrelated donor cohorts were observed.

Selected CD34 blood cell allografts for older patients: low transplant-related mortality, graft failure and acute GvHD

BACKGROUND

Early transplant mortality is related to acute GvHD, which this study in older patients (40 to 60 years) decreased by reducing the graft T-cell number while maintaining a high CD34 cell number--by positive CD34 cell selection. Potential increased risk of relapse is addressed by giving donor leucocyte infusion (DLI) post-transplant.

METHODS

CD34 cells selected by Isolex devices from leukophereses obtained from Filgrastim-treated matched sibling donors were transplanted and DLI given later if there was no GvHD.

RESULTS

Selection of CD34 cells achieved a median of 5.2 million cells/kg, with minimum target for transplantation achieved in 17 of 21 donors. Median CD3 cell number was 0.24 million/kg. Engraftment was rapid and graft failure rare. Transplant-related mortality was low (6% at 3 months). Acute GvHD of >or=Grade 2 occurred in only two patients (12.5%). DLI were given to only six patients who had resolved Grade 1 or no GvHD. Eight of the 17 patients relapsed, including three of the six who had DLI. Extensive chronic GvHD developed in six of 12 evaluable patients, two of these had received DLI. Seven of the 17 patients (41%) are alive at median follow-up of 56 months.

CONCLUSION

CD34 selection allows transplantation of high numbers of CD34 cells with low CD3 cell count, reducing early mortality in patients 40-60 years old because of rapid hemopoietic reconstitution and low acute GvHD incidence. Administration of DLI was often precluded by low-grade acute GvHD.

An outbreak of respiratory syncytial virus infection in a bone marrow transplant unit: effect on engraftment and outcome of pneumonia without specific antiviral treatment

Immunocompromised haematological patients are at high risk for severe, often fatal, respiratory syncytial virus (RSV) pneumonia. In the 2001 winter season, 16 of 195 (8.2%) adult haematological in-patients were diagnosed with RSV infection. Eight patients had undergone stem cell transplantation. The median age was 53 years (range 20-67). A total of 11 patients had nosocomial RSV infection while the rest (five) had community-acquired infection. All patients were febrile and had upper respiratory tract infection (URTI). Eight patients (50%) developed lower RTI. Two of the 16 patients (12.5%) died of respiratory failure, due to the RSV pneumonia, despite ICU admission and supportive ventilation. None of the studied patients received ribavirin therapy or specific RSV immunoglobulin. Two patients autografted for multiple myeloma (MM) showed delayed neutrophil and platelet engraftment despite receiving an adequate dose of stem cells. A third patient undergoing a CD34+ selected HLA-matched sibling mini-allograft for relapsed MM showed graft failure shortly after RSV infection. In our series, RSV infection was concurrent with an outbreak in the community. Unlike other published series, no specific antiviral treatment for RSV pneumonia was used and yet the overall outcome in our patients was favourable. Furthermore, RSV infection in the pre-engraftment period after autologous transplantation was associated with delayed engraftment.

Immunoglobulin kappa light chain gene alleles are not associated with primary Sjögren's syndrome

The immunoglobulin kappa (Km) light chain gene is polymorphic and is believed to play a role in the pathology of infectious and autoimmune diseases. Polymorphisms within the constant region of the Km gene encode three alleles designated Km1, Km1,2 and Km3. Previous studies using serological detection of Km allotypes reported associations between specific Km allotypes, systemic lupus erythematosus and the presence of anti-La antibodies, yet these findings were not confirmed in other studies. In order to more precisely define any associations between Km alleles and anti-Ro/La antibodies we used the polymerase chain reaction and restriction fragment length polymorphisms for Km genotyping in a large cohort of patients with primary Sjögren's syndrome (SS). No associations were observed between specific Km alleles and primary SS when compared with a control population, nor within serologically defined subsets of SS patients. We conclude that Km alleles are not associated with primary SS or the Ro/La autoantibody response.

Successful salvage of RAEB/AML relapsing early post allograft with FLAG-Ida conditioned mini-allograft: a report of two cases

Management options are often limited for patients with AML or high grade myelodysplasia (MDS) relapsing within a year of allogeneic transplantation. We report, in two such patients, the use of re-induction with FLAG-Ida chemotherapy, followed by the infusion of GCSF-mobilized blood stem cells from the same HLA-matched donor. Both patients achieved durable complete remissions with good quality of life and longer disease-free survival than after the first myeloablative allografts. This mini-allograft approach offers a practical, well-tolerated salvage and a potentially curative treatment for relapsed AML/high grade MDS patients failing a first conventional myeloablative allogeneic transplants.

Short Report: Engraftment of T-cell-depleted allogeneic haematopoietic stem cells using a reduced intensity conditioning regimen

Graft-versus-host disease (GVHD) remains a significant complication in patients undergoing allogeneic stem cell transplantation (SCT) using a reduced intensity conditioning regimen. Although T-cell depletion (TCD) reduces the risk of GVHD after a myeloablative conditioning regimen, it is associated with an increased risk of graft failure. We have therefore examined whether TCD compromises engraftment using a fludarabine-based conditioning regimen. Fifteen patients have been transplanted using such a regimen of whom 13 underwent ex vivo TCD. All but one patient demonstrated durable engraftment and no patient receiving a TCD product developed severe GVHD. Thus, TCD may play a role in GvHD prophylaxis using such regimens.

HFE genotypes and haemochromatosis: quantifying the risks of disease

Hereditary haemochromatosis (HH) is an autosomal recessive disease involving mutations in the recently characterised HFE gene linked to HLA-A in the major histocompatibility complex. The known HFE polymorphisms include the wild-type allele, a G-->A substitution at base 845 (845A) and a C-->G substitution at position 187 (187G). Although most cases of HH are accountable by homozygosity of the 845A allele the exact risk of other HFE genotypes, especially those involving the 187G allele has not been determined. We have compiled estimates of disease risk for all known HFE genotypes by re-analyzing published studies. The data show a hierarchical risk calculated as odds ratio (OR) for each genotype 845A/ 845A (OR=2101); 845A/187G (OR=24); 187G/187G (OR=9); 845A/Wt (OR=5); 187G/Wt (OR=2). Interestingly, the disease risk of 187G-genotypes suggests that subtle functional changes in the HFE product can interact with other genetic factors (e.g. trans allele, gender) and environmental factors (e.g. diet) to manifest either as clinical disease, altered iron stores or a normal phenotype. This paradigm is potentially useful in understanding the contribution of HLA alleles to risk of various disorders especially autoimmunity.

The DD genotype of the angiotensin-converting enzyme gene occurs in very low frequency in Australian Aboriginals

BACKGROUND

The DD genotype of the angiotensin-converting enzyme (ACE) gene appears to be an independent risk factor for myocardial infarction, left ventricular hypertrophy and an increased incidence and rate of progression of renal disease. The high incidence of renal disease and end-stage renal failure in the Australian Aboriginal population has prompted investigation of ACE genotypes in these people.

METHODS

ACE genotypes were determined in four groups: (i) normal Australian Caucasian blood donors (n = 100), (ii) Caucasian renal transplant recipients (n = 173), (iii) normal Australian Aboriginals from a single tribe (n = 184), and (iv) Australian Aboriginals included in the renal-transplant programme (n = 94).

FINDINGS

The D allele frequency in the normal Australian Caucasian (54.5%) and renal transplant groups (57.2%) was similar. However, the D allele frequency in the normal Australian Aboriginal (3%) and Aboriginal renal patient group (14.4%) was significantly lower than both Caucasian groups.

INTERPRETATION

The D allele of the ACE gene has little or no influence on the renal disease of Australian Aboriginals.

Fludarabine-based non-myeloablative chemotherapy followed by infusion of HLA-identical stem cells for relapsed leukaemia and lymphoma

Many patients have not been offered potentially curative allogeneic marrow transplants because of the toxicity of myeloablative regimens in the setting of advanced age or organ dysfunction. We treated five patients, ineligible for myeloablative chemotherapy due to one of these criteria, with fludarabine-based non-myeloablative chemotherapy followed by reinfusion of G-CSF-mobilised allogeneic peripheral blood progenitor cells (PBPC). Two patients died early of multi-organ failure. Another patient with massive splenomegaly was infused with a suboptimal number of PBPC; no engraftment was documented. The remaining two patients demonstrated mixed chimerism early post-transplant, but by 3 and 6 months respectively, engraftment was almost entirely of donor origin. One of these patients, transplanted with relapsed AML, remains in remission with extensive chronic GVHD at 17 months. The other patient, transplanted with chemorefractory mantle cell lymphoma, progressed early post-transplant but entered remission coincident with the onset of severe GVHD following cessation of cyclosporin A, suggesting a powerful graft-versus-mantle cell lymphoma effect. These preliminary observations suggest this approach results in engraftment and GVHD/graft-versus-tumour effects similar to myeloablative regimens and may provide an alternative in patients ineligible for conventional conditioning regimens.

Correlation of CD44 expression with proliferative activity of normal human breast epithelial cells in culture

A number of studies have shown that certain variant isoforms of CD44 are overexpressed in human breast cancer, suggesting their use as indicators of the presence of malignant cells. We now show that CD44 isoform mRNA and protein expression is upregulated in normal human breast epithelial cells (HBEC) when these cells are stimulated to proliferate in culture. Reverse transcription-PCR analysis of cultured normal HBEC revealed complex patterns of CD44 mRNA expression that were indistinguishable from patterns previously shown to be characteristic of tissue samples containing malignant HBEC. CD44v6-expressing cells were identified in cultures generated from FACS-purified populations of either normal luminal (CALLA-MUC-1+) or myoepithelial (CALLA+MUC-1-) cells, even though immunohistochemical analysis of normal breast tissue sections confirmed CD44v6 expression to be limited to the myoepithelium in vivo. Increased expression of both CD44v mRNA and protein in cultured populations of normal HBEC was shown to correlate positively with the proportion of cells that were proliferating (Ki-67+) independent of cell density. These results indicate that activation of CD44 variant isoform expression in HBEC occurs as a normal response to factors that stimulate their proliferation and suggests caution in the use of this marker to identify malignant cells.

HLA-identical sibling peripheral blood cell transplants. The Australian experience and preliminary results of a randomised study

Twenty-seven patients undergoing matched sibling BMT were randomly assigned to be infused with bone marrow alone or bone marrow supplemented with allogeneic peripheral blood cells collected by apheresis after stimulation with filgrastim. Other transplant conditions were standard and identical for the two groups. There was no difference between the groups in survival or acute or chronic GVHD, however, the patients receiving blood cells had significantly more rapid neutrophil engraftment by a median of 2 days. We conclude that filgrastim-mobilised HLA-identical sibling allogeneic blood cells are biologically active and safe.

Early cyclosporine taper in high-risk sibling allogeneic bone marrow transplants

Graft-versus-tumour reactions as a form of adoptive immunotherapy may help prevent the recurrence of haematological malignancy following allogeneic BMT. We hypothesised that such reactions may be maximised by shortening the duration of post-transplant immunosuppression by a rapid taper of cyclosporine (CYA). CYA dose was tapered between days 30 and 60 in patients at high risk of relapse, provided there was no evidence of prior significant acute GVHD. Twenty-six of 58 high-risk patients eligible at the time of transplant were subsequently tapered. Seven (27%) developed grade III/IV acute GVHD after completion of the taper, which was fatal in one patient. Chronic GVHD was observed in most patients, although with minimal overall impact on performance status. The overall probability of survival at 2 years was 43%. This non-randomised experience indicates that a rapid taper of CYA is tolerable and may provide an alternative to immunotherapy with donor leukocyte infusion in the high-risk allograft setting.

Isolation and analysis of different subpopulations of normal human breast epithelial cells after their infection with a retroviral vector encoding a cell surface marker

The use of gene transfer procedures has greatly facilitated the investigation of cell lineage relationships and other developmental processes in a variety of primary tissues. In this report we described the infection and selection of primary human breast epithelial cells using retroviral vectors (Jzen-HSA-NEO and MSCV-HSA.NEO) containing the complete 228 bp coding sequence of a murine cell surface marker (Heat Stable Antigen, HSA) as well as the neomycin resistance (neo(r)) gene. Expression of the transduced HSA gene was detectable using either flow cytometry or immunohistochemistry after staining cells with an anti-murine HSA-specific antibody (M1/69). Expression of the transduced neo(r) gene conferred resistance to G418. In initial experiments with the MCF-7 breast cancer cell line, continued expression of both markers was demonstrated in a high proportion of cells for at least 4 weeks after their infection by positive M1/69 staining of cells that had been selected by prior incubation in G418. Evidence of gene transfer to early stage (< 9 days old) primary cultures of normal human breast epithelial cells (15 experiments with cells from 12 normal individuals) was also obtained using an infection protocol in which these calls were exposed to helper-free viral supernatants (2 incubations, 4 to 6 hr each) after being subcultured for 12 to 18 hr to increase their rate of proliferation. The presence of 5-50% (mean = 26%) HSA+ cells was demonstrated in these experiments within 5 days after their infection and the HSA+ populations included both myoepithelial and luminal phenotypes. The transduced (HSA+) cells within both of these subpopulations could also be separately isolated by FACS and subcultured. These results should provide an important starting point for future studies of genetically modified or marked primary human breast epithelial cell populations.

Factors influencing the outcome of donor marrow transplantation in adults from less than ideal donors: experience from two Australian centres

BACKGROUND

This paper reports the results of 78 marrow transplants in two Australian hospitals between 1991 and 1996, using unrelated (n = 54) or mismatched related (n = 24) donors. Twenty-six patients received granulocyte-macrophage colony stimulating factor (GM-CSF) post-transplant as part of a phase II study. Fifty-four patients (74%) had advanced disease.

AIMS

To identify factors associated with a superior outcome post-transplant, to evaluate the effect of GM-CSF on engraftment and other transplant parameters, and to compare the overall results with those of published series.

METHODS

Review of patient records, a Medline search of the relevant literature and appropriate statistical analysis.

RESULTS

The probability of overall survival and event-free survival (EFS) at three years was 35 +/- 6% and 22 +/- 6% respectively. Pre-transplant factors significantly associated with an inferior EFS were advanced disease, poorer performance status and age > 30 years. The EFS in patients with standard risk disease was 51 +/- 13% versus 10 +/- 5% in patients with advanced disease, p < 0.0001. Severe acute graft-versus-host disease was also associated with a poorer outcome. Neutrophil engraftment was faster in patients who received GM-CSF but there was no difference in any other transplant parameters.

CONCLUSIONS

These results are consistent with reported series elsewhere and suggest that an extended family or unrelated donor transplant should generally be limited to patients with a good performance status and early phase but otherwise incurable haematological disease.

G-CSF stimulated donor granulocyte collections for prophylaxis and therapy of neutropenic sepsis

BACKGROUND

The administration of granulocyte colony-stimulating factor (G-CSF) increases the granulocyte count in normal donors and enables the collection of large numbers of mature myeloid cells by leukapheresis. This has potential value in the treatment of sepsis unresponsive to antibiotics in patients with severe neutropenia.

AIM

To evaluate the tolerability of granulocyte collections in normal donors receiving G-CSF, the optimal method of collection and the clinical factors influencing the efficacy of granulocyte infusions.

METHODS

Analysis of the outcome of 55 granulocyte collections from 26 donors for progressive bacterial or fungal sepsis in neutropenic patients (n = 8) or as prophylaxis in patients with recent fungal infections undergoing allogeneic bone marrow transplantation (BMT) (n = 3).

RESULTS

G-CSF was well tolerated in most donors. Fatigue occurred commonly after the second collection. The median WCC per 200-220 mL bag was 351 x 10(9)/L. Collections were optimised with the use of a sedimenting agent (dextran) and a deepened interface setting on the cell separator. There was only a weak correlation between the number of granulocytes infused and the increment in the patient, but levels were usually maintained > or = 0.5 x 10(9)/L for the next 24 hours. The infusions were successful in three septic patients without multi-organ dysfunction and prophylactically, in two patients with localised fungal infections undergoing MBT. The infusions were not beneficial in patients with septicaemia and established organ dysfunction or with extensive pulmonary aspergillosis.

CONCLUSIONS

G-CSF mobilised granulocyte collections are feasible and the preliminary evidence suggests that the infusion of these cells may be useful early in the prophylaxis or treatment of severe neutropenic sepsis.

Acute portal vein thrombosis after autologous stem cell transplantation

Three patients developed abdominal pain and abnormal liver enzymes without hyperbilirubinemia, early after autografting for lymphoma. Two had received conditioning therapy with busulfan, cyclophosphamide and continuous infusion etoposide; the other had received busulfan and melphalan. Doppler ultrasound in all cases demonstrated thrombosis of the main portal vein and its branches. In the two patients tested, transient deficiencies in protein C (both cases) and protein S (one case) were observed. One case was chronologically related to anti-fibrinolytic therapy and resolved spontaneously. The other two cases resolved after treatment with low molecular weight heparin. Portal vein thrombosis should be considered in the differential diagnosis of abdominal pain and liver dysfunction after BMT.

Rapid and efficient selection of human hematopoietic cells expressing murine heat-stable antigen as an indicator of retroviral-mediated gene transfer

Recombinant retroviruses offer many advantages for the genetic modification of human hematopoietic cells, although their use in clinical protocols has thus far given disappointing results. There is therefore an important need to develop new strategies that will allow effectively transduced primitive hematopoietic target populations to be both rapidly characterized and isolated free of residual nontransduced but biologically equivalent cells. To address this need, we constructed a murine stem cell virus (MSCV)-based retroviral vector containing the 228-bp coding sequence of the murine heat-stable antigen (HSA) and generated helper virus-free amphotropic MSCV-HSA producer cells by transfection of GP-env AM12 packaging cells. Light density and, in some cases, lineage marker-negative (lin-) normal human marrow or mobilized peripheral blood cells preactivated by exposure to interleukin-3 (IL-3), IL-6, and Steel factor in vitro for 48 hours were then infected by cocultivation with these MSCV-HSA producer cells for a further 48 hours in the presence of the same cytokines. Fluorescence-activated cell sorting (FACS) analysis of the cells 24 hours later showed 21% to 41% (mean, 27%) of those that were still CD34+ to have acquired the ability to express HSA. The extent of gene transfer to erythroid and granulopoietic progenitors (burst-forming unit-erythroid and colony-forming unit-granulocyte-macrophage), as assessed by the ability of these cells to form colonies of mature progeny in the presence of normally toxic concentrations of G418, averaged 11% and 12%, respectively, in 6 experiments. These values could be increased to 100% and 77%, respectively, by prior isolation of the CD34+HSA+ cell fraction and were correspondingly decreased to an average of 2% and 5%, respectively, in the CD34+HSA- cells. In addition, the extent of gene transfer to long-term culture-initiating cells (LTC-IC) was assessed by G418 resistance. The average gene transfer to LTC-IC-derived colony-forming cells in the unsorted population was < or = 7% in 4 experiments. FACS selection of the initially CD34+HSA+ cells increased this value to 86% and decreased it to 3% for the LTC-IC plated from the CD34+HSA- cells. Transfer of HSA gene expression to a phenotypically defined more primitive subpopulation of CD34+ cells, ie, those expressing little or no CD38, could also be shown by FACS analysis of infected populations 24 hours after infection. These findings underscore the potential use of retroviral vectors encoding HSA for the specific identification and non-toxic selection immediately after infection of retrovirally transduced populations of primitive human hematopoietic cells. In addition, such vectors should facilitate the subsequent tracking of their marked progeny using multiparameter flow cytometry.

The optimization of collection of peripheral blood stem cells for autotransplantation in acute myeloid leukaemia

Between November 1982 and November 1986 31 patients with acute myeloid leukaemia underwent peripheral blood stem cell apheresis during haemopoietic regeneration following induction chemotherapy. A retrospective analysis of the factors affecting the efficacy of stem cell harvest and of the clinical outcome of these patients was performed. The mean number of myeloid progenitor cells (CFU-GM) collected was significantly higher in the complete remission group (n = 22) than in the partial remission group (n = 9). Fifty x 10(4) CFU-GM/kg body weight or more, which produced rapid, complete and sustained haemopoietic reconstitution after autografting in our patients, were collected from six of nine patients who underwent three or four 7-litre aphereses over 5-7 days using a lymphocyte collection procedure on the Fenwal CS3000 [Protocol B] but only from two of 12 patients who underwent three or four 5-litre aphereses over 3-5 days using the Aminco Celltrifuge [Protocol A] (p less than 0.05). No adverse effects on the rates of neutrophil, platelet and lymphocyte recovery after induction chemotherapy or on long-term disease-free survival for patients who achieved a complete remission could be attributed to apheresis when compared with a historical control group of 39 patients who achieved complete remission following the same induction chemotherapy but did not undergo apheresis. We conclude that sufficient numbers of peripheral blood stem cells to produce safe and rapid haemopoietic reconstitution can be collected from most patients who achieve complete remission using apheresis Protocol B without impairment of haemopoietic recovery or adversely affecting the length of complete remission.