Natural killer cell alloreactivity and haplo-identical hematopoietic transplantation

In haplo-identical hematopoietic transplantation, donor vs. recipient natural killer (NK) cell alloreactivity derives from a mismatch between donor NK clones bearing inhibitory killer cell Ig-like receptors (KIR) for self-HLA class I molecules and their HLA class I ligands (KIR ligands) on recipient cells. When faced with mismatched allogeneic targets, these NK clones sense the missing expression of self-HLA class I alleles and mediate alloreactions. KIR ligand mismatches in the GvH direction trigger donor vs. recipient NK cell alloreactions, which improve engraftment, do not cause GvHD and control relapse in AML patients . The mechanism whereby alloreactive NK cells exert their benefits in transplantation has been elucidated in mouse models. The infusion of alloreactive NK cells ablates (i) leukemic cells, (ii) recipient T cells that reject the graft and (iii) recipient DC that trigger GvHD, thus protecting from GvHD.

Alternative donor transplants for adult acute lymphoblastic leukaemia: a comparison of the three major options

Myeloablative sibling-matched allogeneic transplantation for adult acute lymphoblastic leukaemia provides the best outcome, but most patients lack a suitable, related histocompatible donor. We reviewed three haematopoietic stem cell donor sources used for alternative donor transplantation pointing out drawbacks of these approaches including inherent selection bias. Matched unrelated donor allografts most often are performed in Philadelphia chromosome-positive disease and in second complete remission (CR2); a nearly 30% event-free survival (EFS) can be anticipated in select patients. Transplants using haploidentical donors are most successful if undertaken in CR1 and CR2 and appear to produce EFS rates of about 25%. Limited umbilical cord blood transplant data suggest efficacy, but marked patient and treatment heterogeneity hamper conclusions. Each of these three strategies has unique potential benefits and disadvantages. The growing use of minimal residual disease detection may identify subgroups of patients unlikely to be cured by chemotherapy alone; these patients are candidates for upfront high-dose chemoradiotherapy and cellular immunotherapy. These three approaches are plagued by treatment-related mortality and relapse rates as high as 40%, but advances in technology and supportive care may make each stem cell source more feasible and efficacious.

Innate immunity against hematological malignancies

BACKGROUND

Allogeneic hematopoietic transplantation relies on T-cell alloreactions for engraftment and the GvL effect. In HLA haplotype-mismatched transplants, extensive T-cell depletion of the graft is essential to prevent GvHD. This raises the question of whether mismatched transplants exert any GvL effect, and whether it will ever be possible to reduce the intensity of preparative regimens. Natural killer (NK) cells are negatively regulated by MHC Class I-specific inhibitory receptors. Mismatched transplants may therefore trigger NK-cell alloreactivity.

METHODS

The effects of NK-cell alloreactivity were evaluated in clinical transplantation and in murine transplant models.

RESULTS

In clinical hematopoietic stem-cell transplants, HLA Class I disparities driving NK-cell alloreactions in the GvH direction eliminate AML relapse and graft rejection, while protecting patients from GvHD. In murine MHC mismatched transplant models, the pre-transplant infusion of donor-versus-recipient alloreactive NK cells conditioned the recipients to BMT, and reduced GvHD.

DISCUSSION

NK-cell alloreactivity may thus provide a novel, powerful tool for enhancing the efficacy and safety of allogeneic hematopoietic transplantation.

Haploidentical stem cell transplantation for acute leukemia

PREMISE

Since March 1993, 133 patients with high-risk acute leukemia (66 AML, 67 ALL) have received a megadose of T-cell depleted hematopoietic stem cells. The 1993-95 conditioning protocol included TBI, thiotepa, ATG and CY for 36 patients who received an inoculum made up of lectin-separated bone marrow and PBPCs. After 1995, to minimise the extra-hematological toxicity of the conditioning and eliminate GvHD, we substituted fludarabine for CY in the conditioning and PBPCs were depleted of T-cells by a positive selection of the CD34+ cells using CellPro (n=44 patients) or, since January 1999, CliniMacs (n = 53 patients). A later modification to the protocol in January 1999 was the suspension of post transplant G-CSF. WORK IN PROGRESS: We report here the results in the last 53 acute leukemia patients all of whom were transplanted under our modified protocol. Ages ranged from 9 to 62 years with a median of 38 years for the 33 patients with AML and 23 for the 20 with ALL. All were at high risk because 25 were actually in relapse at transplant, 16 were in second or later CR and even the 12 patients in CR1 were at high risk because of the unfavourable prognostic features. Overall 52/53 patients (98%) engrafted. The TBI-Fludarabine-based conditioning was well tolerated even in the 14 patients between 45 and 62 years of age. There was no veno-occlusive disease of the liver and the incidence of severe mucositis was low. Even though no post-transplant immunosuppressive therapy was given, acute GvHD grade > or = II occurred in only 4 cases and only one progressed to chronic GvHD. Overall, 16 patients (30%) have died of non-leukemic causes. Relapses occurred mainly in patients who were already in relapse at transplant (12/25). Only 3 of the 28 who were in any CR at transplant have so far relapsed. As our group has already shown, donor-vs-recipient NK cell alloreactivity exerts a specific graft-vs-AML effect in the absence of GvHD. In fact, leukemia relapse was largely controlled in AML recipients whose donor was NK alloreactive, with only 2 out of 16 relapsing. To date, 13 of 18 AML (72%) and 5 of 10 ALL (50%) who were in any CR at transplant, survive disease-free while 4 of the 15 patients (16%) in relapse at transplant survive. The probability of event-free survival for patients transplanted in CR is 60% in the 18 AML patients and 38% in the 10 ALL. The probability of EFS was significantly better in the 16 AML patients whose transplant included donor vs recipient NK cell alloreactivity than in those whose transplant did not (70% vs 7%). In conclusion, given our current results, the most suitable candidate for the full haplotype mismatched transplant should be in early stage disease and selection of an NK alloreactive donor is recommended.

Cataracts in patients receiving stem cell transplantation after conditioning with total body irradiation

One hundred and ninety-three patients with hematological malignancies and a follow-up > or =1 year, treated with stem cell transplantation (45 autologous, 99 allogeneic T cell-depleted matched, 49 allogeneic T cell-depleted mismatched) from July 1985 to May 1998, were considered evaluable for the development of cataracts. Total body irradiation (TBI), administered either according to a hyperfractionated scheme (HTBI) or in a single dose (STBI), was employed in the conditioning regimens. HTBI was prescribed in 94% of patients undergoing allogeneic matched transplant, while STBI was used in 71% of patients receiving allogeneic mismatched and in all patients undergoing autologous transplant. The median follow-up was 7.56 years in the HTBI and 3.02 years in the STBI group. Among the different risk factors analyzed by univariate analysis only the TBI scheme and type of transplant reached statistical significance (P < 0.0001 and P < 0.001, respectively). By multivariate analysis only the TBI scheme was an independent factor for cataract development (STBI vs HTBI RR 7.2; P < 0.01). Our results showed that STBI is more cataractogenic than HTBI. The incidence of cataract we observed was among the lowest described in the literature. T cell depletion, because it prevents graft-versus-host disease and reduces the protracted use of post-transplant steroids, explains the results we obtained.

Haploidentical stem cell transplantation in leukemia

In acute leukemia patients, infusing a megadose of extensively T-cell-depleted hematopoietic stem cells after an immuno-myeloablative conditioning regimen ensures sustained engraftment of full-haplotype mismatched transplants without graft-vs-host disease. Besides the conditioning regimen and the megadose of stem cells donor natural killer cell alloreactivity also plays a role in facilitating engraftment and in preventing relapse. Since our first successful pilot study, our efforts have concentrated on developing new conditioning regimens, optimizing the graft processing and improving the post-transplant immunological recovery. The results we have so far achieved in 112 very high-risk acute leukemia patients show that haploidentical transplantation is now a clinical reality. Because virtually all patients in need of a hematopoietic stem cell transplant have a full-haplotype mismatched donor, who is immediately available, a T-cell depleted mismatched transplant should be offered, not as a last resort, but as a viable option to high risk acute leukemia patients who do not have, or cannot find, a matched donor.

Allogeneic transplantation across the HLA barriers

In high-risk acute leukemia patients, a 10-fold increase in the dose of extensively T-cell-depleted hematopoietic stem cells ensures sustained full-donor engraftment of one-haplotype-mismatched transplants without graft-vs.-host disease. Since our first successful pilot study, which exploited the principle of a megadose stem cell transplant, our efforts have concentrated on developing new conditioning regimens, optimizing graft processing and improving the post-transplant immunologic recovery. The results so far achieved in more than 100 high-risk acute leukemia patients show that haploidentical transplantation is now a clinical reality. Because virtually all patients in need of a hematopoietic stem cell transplant have a full-haplotype-mismatched family donor, a T-cell-depleted mismatched transplant can be offered with curative intent, thus extending allogeneic transplantation procedures to virtually all candidates.

Postgrafting administration of granulocyte colony-stimulating factor impairs functional immune recovery in recipients of human leukocyte antigen haplotype-mismatched hematopoietic transplants

In human leukocyte antigen haplotype-mismatched transplantation, extensive T-cell depletion prevents graft-versus-host disease (GVHD) but delays immune recovery. Granulocyte colony-stimulating factor (G-CSF) is given to donors to mobilize stem cells and to recipients to ensure engraftment. Studies have shown that G-CSF promotes T-helper (Th)-2 immune deviation which, unlike Th1 responses, does not protect against intracellular pathogens and fungi. The effect of administration of G-CSF to recipients of mismatched hematopoietic transplants with respect to transplantation outcome and functional immune recovery was investigated. In 43 patients with acute leukemia who received G-CSF after transplantation, the engraftment rate was 95%. However, the patients had a long-lasting type 2 immune reactivity, ie, Th2-inducing dendritic cells not producing interleukin 12 (IL-12) and high frequencies of IL-4- and IL-10-producing CD4(+) cells not expressing the IL-12 receptor beta(2) chain. Similar immune reactivity patterns were observed on exposure of donor cells to G-CSF. Elimination of postgrafting administration of G-CSF in a subsequent series of 36 patients with acute leukemia, while not adversely affecting engraftment rate (93%), resulted in the anticipated appearance of IL-12-producing dendritic cells (1-3 months after transplantation versus > 12 months in transplant recipients given G-CSF), of CD4(+) cells of a mixed Th0/Th1 phenotype, and of antifungal T-cell reactivity in vitro. Moreover, CD4(+) cell counts increased in significantly less time. Finally, elimination of G-CSF-mediated immune suppression did not significantly increase the incidence of GVHD (< 15%). Thus, this study found that administration of G-CSF to recipients of T-cell-depleted hematopoietic transplants was associated with abnormal antigen-presenting cell functions and T-cell reactivity. Elimination of postgrafting administration of G-CSF prevented immune dysregulation and accelerated functional immune recovery.

Total body irradiation-based regimen in the conditioning of patients submitted to haploidentical stem cell transplantation

BACKGROUND AND PURPOSE

To evaluate the efficacy and toxicity of a highly immuno- and myelo-suppressive conditioning regimen followed by the infusion of large numbers of T-cell-depleted mismatched haematopoietic stem cells in 43 high-risk acute leukaemia patients.

RESULTS

A high rate of engraftment (95%) and no graft-versus-host disease (GvHD) were observed. The 4-year probability of event-free survival was 0.25+/-0.09 for acute myeloid leukaemia and 0.17+/-0.07 for acute lymphoid leukaemia patients.

CONCLUSIONS

This study shows that the main obstacles limiting the use of mismatched transplants, i.e. GvHD and rejection, were overcome.

Limited engraftment capacity of bone marrow-derived mesenchymal cells following T-cell-depleted hematopoietic stem cell transplantation

The engraftment capacity of bone marrow-derived mesenchymal cells was investigated in 41 patients who had received a sex-mismatched, T-cell-depleted allograft from human leukocyte antigen (HLA)-matched or -mismatched family donors. Polymerase chain reaction (PCR) analysis of the human androgen receptor (HUMARA) or the amelogenin genes was used to detect donor-derived mesenchymal cells. Only 14 marrow samples (34%) from 41 consenting patients generated a marrow stromal layer adequate for PCR analysis. Monocyte-macrophage contamination of marrow stromal layers was reduced below the levels of sensitivity of HUMARA and amelogenin assays (5% and 3%, respectively) by repeated trypsinizations and treatment with the leucyl-leucine (leu-leu) methyl ester. Patients who received allografts from 12 female donors were analyzed by means of the HUMARA assay, and in 5 of 12 cases a partial female origin of stromal cells was demonstrated. Two patients who received allografts from male donors were analyzed by amplifying the amelogenin gene, and in both cases a partial male origin of stromal cells was shown. Fluorescent in situ hybridization analysis using a Y probe confirmed the results of PCR analysis and demonstrated in 2 cases the existence of a mixed chimerism at the stromal cell level. There was no statistical difference detected between the dose of fibroblast progenitors (colony-forming unit-F [CFU-F]) infused to patients with donor- or host-derived stromal cells (1.18 +/- 0.13 x 10(4)/kg vs 1. 19 +/- 0.19 x 10(4)/kg; P >/=.97). In conclusion, marrow stromal progenitors reinfused in patients receiving a T-cell-depleted allograft have a limited capacity of reconstituting marrow mesenchymal cells.

Interphase FISH for Y chromosome, VNTR polymorphisms, and RT-PCR for BCR-ABL in the monitoring of HLA-matched and mismatched transplants

Thirty-six sex-mismatched transplants were studied using fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) methods. Molecular cytogenetics was performed using interphase FISH with a centromeric probe for chromosome Y, and PCR amplification was performed with a set of VNTR microsatellite loci. In addition, reverse transcriptase-PCR (RT-PCR) for BCR-ABL fusion was used to investigate cases of Philadelphia chromosome (Ph)-positive chronic myeloid leukemia (CML) and acute lymphoblastic leukemia (ALL). Our integrated approach of post-transplant monitoring was helpful in documenting successful transplants and in controlling the size of Ph-positive clones in CML. A striking overlap was found between results from FISH analysis and PCR for polymorphic loci.

Peripheral blood progenitor cell mobilization in healthy donors receiving recombinant human granulocyte colony-stimulating factor

OBJECTIVE

We analyzed the incidence of primitive (LTC-IC) and committed (CFU-mix, BFU-E, CFU-GM) hematopoietic progenitors detected under steady-state conditions and upon progenitor cell mobilization in a cohort of healthy donors receiving recombinant human granulocyte colony-stimulating factor (rhG-CSF).

MATERIALS AND METHODS

Healthy donors (n = 30) of HLA-mismatched or -matched stem cell transplants were mobilized with rhG-CSF (8 microg/Kg body weight subcutaneously twice daily until completion of leukapheresis). PBPC collections were started after 4 days of rhG-CSF therapy.

RESULTS

Steady-state incidence of bone marrow LTC-IC, but not committed progenitors, significantly correlated with the numbers of mobilized CD34+ cells (r = 0.6, p = 0.004), CFU-GM (r = 0.79, p = 0.0005) and CFC (r = 0.76, p = 0.001) detected after 4 days of rhG-CSF therapy. Statistically significant correlations were also found between steady-state blood CFU-GM and peak numbers of CD341 cells (r = 0.68, p = 0.001), numbers of day 4 CD341 cells (r = 0.52, p = 0.005), CFU-GM (r = 0.63, p = 0.002), and CFC (r = 0.61, p = 0.003).

CONCLUSION

Our data show that in normal volunteers baseline marrow LTC-IC and blood CFU-GM correlate with rhG-CSF-mobilized PBPC. The potential clinical relevance of these findings in the identification of poor mobilizers will be tested in a prospective study.

Fatal herpesvirus-6 encephalitis in a recipient of a T-cell-depleted peripheral blood stem cell transplant from a 3-loci mismatched related donor

Human herpesvirus-6 (HHV-6), like all the other herpes viruses, remains latent in host cells after primary infection but can be reactivated in immunocompromised patients causing fever, skin rash, bone marrow (BM) suppression, pneumonitis, sinusitis and meningoencephalitis. We describe the case of a man with chronic myelogenous leukemia who developed encephalitis associated with acute graft-versus-host disease two months after a T-cell-depleted mismatched peripheral blood stem cell transplant. Magnetic resonance images of the brain revealed multiple bilateral foci of signal abnormality. HHV-6 was the only pathogen detected in cerebrospinal fluid by PCR. Treatment with both ganciclovir and foscarnet was unsuccessful and the patient gradually deteriorated and died. Other cases of HHV-6 encephalitis after bone marrow transplantation are reviewed.

Improved outcome with T-cell-depleted bone marrow transplantation for acute leukemia

PURPOSE

To eliminate the risk of rejection and lower the risk of relapse after T-cell-depleted bone marrow transplants in acute leukemia patients, we enhanced pretransplant immunosuppression and myeloablation.

PATIENTS AND METHODS

Antithymocyte globulin and thiotepa were added to standard total-body irradiation/cyclophosphamide conditioning. Donor bone marrows were depleted ex vivo of T lymphocytes by soybean agglutination and E-rosetting. This approach was tested in 54 consecutive patients with acute leukemia who received transplants from HLA-identical sibling donors or, in two cases, from family donors mismatched at D-DR. No posttransplant immunosuppressive treatment was given as graft-versus-host disease (GVHD) prophylaxis.

RESULTS

Neither graft rejection nor GVHD occurred. Transplant-related deaths occurred in six (16.6%) of 36 patients in remission and in seven (38.8%) of 18 patients in relapse at the time of transplantation. The probability of relapse was .12 (95% confidence interval [CI], 0 to .19) for patients with acute myeloid leukemia and .28 (95% CI, .05 to .51) for patients with acute lymphoblastic leukemia who received transplants at the first or second remission. At a median follow-up of 6.9 years (minimum follow-up, 4.9 years), event-free survival for patients who received transplants while in remission was .74 (95% CI, .54 to .93) for acute myeloid leukemia patients and .59 (95% CI, .35 to .82) for acute lymphoblastic leukemia patients. All surviving patients have 100% performance status.

CONCLUSION

Adding antithymocyte globulin and thiotepa to the conditioning regimen prevents rejection of extensively T-cell-depleted bone marrow. Even in the complete absence of GVHD, the leukemia relapse rate is not higher than in unmanipulated transplants.

The role of megadose CD34+ progenitor cells in the treatment of leukemia patients without a matched donor and in tolerance induction for organ transplantation

Throughout the 1980s, transplantation of unmodified (T cell-replete) bone marrow from full haplotype incompatible family donors was associated with an unsuccessful outcome because of graft failure and severe graft-versus-host disease (GVHD), at times affecting up to 90% of recipients. Although extensive T cell depletion of donor bone marrow was successful in preventing GVHD in children with severe combined immunodeficiency disease (SCID), results were disappointing in leukemic patients because the benefit of preventing GVHD was offset by graft failure. Resistance to engraftment appears to be mediated by host-derived cytotoxic T-lymphocyte precursors that survive supralethal conditioning. In the present paper, we review data that show that these genetic histocompatibility barriers can be overcome in stringent mouse models, employing lethally as well as sublethally irradiated recipients, by two major approaches that are synergistic to each other: escalation of hematopoietic progenitor cell dose and the use of nonalloreactive T cells. The former approach is already being successfully implemented in the treatment of leukemic patients.

Mismatched T cell-depleted hematopoietic stem cell transplantation for children with high-risk acute leukemia

The aim of this study was to extend allogeneic hematopoietic stem cell transplantation to leukemia patients without a matched donor. To prevent graft failure, large doses of T cell-depleted hematopoietic stem cells were transplanted following a highly myeloablative and immunosuppressive conditioning regimen. Fifteen children with high-risk acute leukemia received T cell-depleted hematopoietic stem cells from full-haplotype mismatched family members after a conditioning regimen that included single-dose TBI, thiotepa, ATG and fludarabine. To prevent GVHD, marrow cells were T-depleted by soybean agglutinin and E-rosetting, peripheral blood cells by E-rosetting followed by positive selection of the CD34+ cells. No post-transplant prophylaxis for GVHD was administered. In all patients full donor-type engraftment was achieved. None of the evaluable patients developed either acute or chronic GVHD. Regimen-related toxicity was minimal. Five patients are alive and event-free at a median follow-up of 18 months (range 13-28). All surviving patients have a good quality of life. Seven patients have relapsed. This study shows that GVHD and graft failure, which limited the use of full-haplotype mismatched bone marrow transplants, have been overcome. Since almost all children have a mismatched relative, advances in this area should make mismatched transplants a routine consideration for patients with high-risk leukemia without a matched related or unrelated donor.

Treatment of high-risk acute leukemia with T-cell-depleted stem cells from related donors with one fully mismatched HLA haplotype

BACKGROUND

In this study we tried to achieve successful transplantation in patients with acute leukemia with the use of hematopoietic stem cells from donors who shared only one HLA haplotype with the recipient (a "full-haplotype mismatch"). To prevent graft failure, large doses of T-cell-depleted hematopoietic stem cells were transplanted after a conditioning regimen of enhanced myeloablation and immunosuppression was administered to the recipient.

METHODS

Forty-three patients with high-risk acute leukemia who were scheduled for transplantation received total-body irradiation, thiotepa, fludarabine, and antithymocyte globulin. The graft consisted of peripheral-blood progenitor cells that had been mobilized in the donor with recombinant granulocyte colony-stimulating factor and also, in 28 cases, bone marrow. Bone marrow from the donor was depleted of T lymphocytes by processing with soybean agglutinin and E-rosetting. T-cell depletion of peripheral-blood mononuclear cells was achieved by E-rosetting followed by positive selection of CD34+ cells. No post-transplantation prophylaxis against graft-versus-host disease (GVHD) was administered.

RESULTS

In all the patients, full donor-type engraftment was achieved. In none of the patients who could be evaluated did acute or chronic GVHD develop. Regimen-related toxicity was minimal. Eleven of the 23 patients with acute lymphoblastic leukemia had a relapse, as did 2 of the 20 patients with acute myeloid leukemia. Transplantation-related mortality was 40 percent. After a median follow-up of 18 months (range, 8 to 30), 12 of the 43 patients were alive and free of disease. All surviving patients had a good quality of life.

CONCLUSIONS

The main limitations of transplantation of bone marrow from donors who are matched with the recipient for only one HLA haplotype GVHD and graft failure - can be overcome. Since most patients have a relative with one haplotype mismatch, advances in this method will increase the availability of hematopoietic-cell transplantation as curative therapy for acute leukemia.

Unrelated donor marrow transplantation for chronic myelogenous leukaemia

Between January 1989 and July 1995 the search for an unrelated donor (UD) was started for 379 consecutive Italian patients with Philadelphia positive (Ph+) chronic myelogenous leukaemia (CML). 89 (23%) were transplanted. The overall probability of transplant before and after December 1991 was 16% and 49%, respectively (P=0.0001), and average interval between search activation and graft was 23 months and 13 months, respectively (P=0.0001). Disease-free survival (DFS) following 60 consecutive transplants performed before February 1996 was 41.5% at 48 months and was 64% for patients grafted after January 1993. In univariate analysis, five variables had a favourable effect on DFS: year of bone marrow transplantation (BMT) after 1993 (P=0.0002), HLA-DRB1 donor/recipient (D/R) match (P=0.0006), total body irradiation (TBI) containing regimen (P=0.0006), graft-versus-host disease (GvHD) prophylaxis including 'early' cyclosporin before the transplant, and a marrow cell dose > 3 x 10(8)/kg of recipient body weight (P=0.04). Multivariate analysis confirmed that HLA identity (P=0.006), TBI-containing regimen (P=0.0001) and 'early cyclosporin' (P=0.04) were associated with higher DFS. Transplant-related mortality (TRM) was 67% in patients grafted before January 1993 and 30% in patients grafted subsequently (P=0.002). Multivariate analysis confirmed DRB1 identity (P=0.03) and TBI-containing regimen (P=0.0005) to be independent factors predictive of low TRM. This suggests that the outcome of patients transplanted from an HLA DRB1 matched donor, after a TBI-containing preparative regimen, is similar to results recently reported in patients transplanted from geno-identical siblings. These results indicate that the search should be initiated at diagnosis for patients < 45 years of age and UD BMT should be considered early in the disease course for those with an available DRB1-matched unrelated donor.

Interstitial pneumonitis in acute leukemia patients submitted to T-depleted matched and mismatched bone marrow transplantation

PURPOSE

To identify factors that could contribute to interstitial pneumonitis (IP), which remains one of the major causes of morbidity and mortality after both matched and mismatched bone marrow transplantation (BMT).

METHODS AND PATIENTS

Ninety acute leukemia patients received an allogeneic T-depleted matched (n = 54) or mismatched (n = 36) BMT. They were preconditioned with total body irradiation (TBI), thiotepa, rabbit anti-thymocyte globulin, and cyclophosphamide. The TBI scheme was hyperfractionated in matched, and a single dose in mismatched patients. The dose to the lungs was reduced in both groups.

RESULTS

Five of the 54 matched patients developed IP. All cases were fatal. There were 16 cases of IP, 13 fatal, in the mismatched group. The probability of developing IP was 11.3 +/- 4.9% and 48.6 +/- 9.0%, respectively. The between-group difference was statistically significant (p < 0.0001). The type of transplant and the TBI scheme were the most important parameters for IP development in univariate analysis, whereas acute graft-versus-host disease, disease stage and sex were nonsignificant. Median follow-up was 342 days (range 17-2900).

CONCLUSIONS

The low incidence of IP in matched patients and the lack of idiopathic cases are evidence for the validity of the TBI schedule. In contrast, the incidence in mismatched patients remains too high; therefore, new strategies should be studied in an attempt to lower it.

Clinical use of allogeneic hematopoietic stem cells from sources other than bone marrow

BACKGROUND AND OBJECTIVE

Peripheral blood stem cells (PBSC) are being increasingly used as an alternative to conventional allogeneic bone marrow (BM) transplantation. This has prompted the Working Group on CD34-Positive Hematopoietic Cells to evaluate the current utilization of allogeneic PBSC in clinical hematology.

EVIDENCE AND INFORMATION SOURCES

The method employed for preparing this review was that of informal consensus development. Members of the Working Group met three times, and the participants at these meetings examined a list of problems previously prepared by the chairman. They discussed the single points in order to reach an agreement on different opinions and eventually approved the final manuscript. Some of the authors of the present review have been working in the field of stem cell transplantation and have contributed original papers in peer-reviewed journals. In addition, the material examined in the present review includes articles and abstracts published in journals covered by the Science Citation Index and Medline.

STATE OF THE ART

Review of the current literature shows that unmanipulated allogeneic PBSC give prompt and stable engraftment in HLA-identical sibling recipients. Despite the much higher number of T-cells infused, the incidence and severity of acute GVHD after PBSC transplant seems comparable to that observed with bone marrow (BM) cells. In comparison to the latter, PBSC probably ensure faster immunologic reconstitution in the early post-transplant period. Controversial results on the incidence and severity of acute-GVHD have been reported when CD34+ selection methods are used. Prospective randomized trials are underway to compare the results of PBSC and BM allogeneic transplantation. In mismatched family donor transplants, T-cell depleted PBSC successfully engraft immune-myeloablated recipients through a megacell-dose effect able to overcome the HLA barrier. Experience with PBSC in the context of unrelated donor transplants is currently anecdotal and prospective trials should be completed before that practice becomes routine. Finally, there is also limited evidence that, following induction chemotherapy, the addition of PBSC to donor lymphocyte infusion (DLI) for treatment of leukemia relapse after BMT may improve the safety and effectiveness of DLI itself. Concerning cord blood (CB) transplants, the most interesting aspects are the ease of CB collection and storage, the low risk of viral contamination and the low immune reactivity of CB cells. This last property has its clinical counterpart in an apparently reduced incidence and severity of acute GVHD both in sibling and unrelated CB transplants, probably making the level of donor/recipient HLA disparity acceptable a greater degree with respect to what is required for transplants from other sources.

Use of stem cells from mismatched related donors

Mismatched haploidentical bone marrow transplantations from a related donor have been the topic of clinical and laboratory research for more than 20 years. During that time, new treatment strategies have been designed based on animal experiments, and, since our group introduced the megadose inoculum which combines T-cell-depleted bone marrow cells with a large number of granulocyte colony-stimulating factor-mobilized peripheral blood stem cells and a more intensive conditioning regimen, have done much to overcome the problems of graft-versus-host disease and graft rejection. As most patients have a full haplotype mismatched relative available, this technique means that a far greater number of patients with hematologic malignancies can be offered a T-cell-depleted transplantation as curative therapy.