Optimizing peripheral blood stem cells transplantation outcome through amend relapse and graft failure: a review of current literature

After chemotherapy with specific agent(s), in order to achieve complete remission (CR), DLI will be initiated based on the following strategies [18]. First, proper considered time of DLI suddested to be 1–2 week after chemotherapy in order to optimize the synergistic effect of chemotherapy and DLI [19]. Although the definite initial dosage is not confirmed, it has been established that high doses (>10 × 10⁷ CD3/kg) can induce more frequent GVHD. Also, previous efforts have not been successful in decreasing the risk of relapse occurrence and improvement of overall survival in the mentioned high doses. The initial dosage should be 1 × 10⁶ CD3/kg which is followed by logarithmic escalation [18‐21]. In this strategy, the maximum and optimal cell dosage are different based on the type of malignancy. In chronic myeloid leukemia (CML) patients, the cell dosage less than 1 × 10⁸ T cells/kg is sub-optimal and doses above 4.5 × 10⁸ T cells/kg might lead to various complications [22‐24]. In acute myeloid leukemia (AML) patients, any cell doses less than 1.5 × 10⁸ T cells/kg may lead to increased rate of failure. In patients with acute lymphoblastic leukemia (ALL), higher response rate was observed in studies using 1–2 × 10⁸ T cells/kg [23, 25, 26]. interestingly, the higher cell doses were associated with lower clinical response rates. In chronic lympho-proliferative disorders such as lymphomas, using DLI in 0.01–1.0 × 10⁸ T cells/kg dosage, higher response rates were observed [27‐29]. Likewise, in multiple myeloma patients, it seems that there is not a well-defined relationship between cell dosages and response rates with DLI. Cell dosages ranged 0.01–8.2 × 10⁸ T cells/kg were used in different clinical trials [30‐32].

5-Azacytidine and DLI can induce long-term remissions in post allograft relapsed AML patients [33]. In this strategy, DLI was performed for transplanted AML and myelodysplastic syndromes (MDS) patients who were under chemotherapy after eight cycles of 5-azacitidine therapy (100 mg/m²/day, days 1–5, every 28 days). After every two cycles of 5-azacitidine, 1–5 × 10⁶ to 1–5 × 10⁸ CD3⁺cells/kg were infused [17, 34].

This method is based on lymphocyte regulatory T cell (T reg) suppression during the LD process [35]. To minimize the risk of severe GVHD incidence, the following strategies could be considered. First, cyclophosphamide (CY) and fludarabine (FLU) should be administered at the doses of 600 mg/m² on day 1 and 25 mg/m²/day on days 1–3, respectively. At the second step, donor lymphocytes were infused in a fixed high dose of 1 × 10⁸ CD3+ cells/kg, 48 h after the last FLU injection. Finally, patients who received chemotherapy along with the DLI (chemo-DLI) showed more frequent episodes acute GVHD, particularly in lower gastro-intestinal (GI) system [35‐37].

When low-dose of DL is requested (10⁴–10⁵ T-cells/kg), small aliquot of freshly collected blood from a related donor are needed. According to National Systems guidelines, if all tests for transfusion transmitted diseases were negative in sample collection time, this product could be readily used for patients. Usually, small aliquots of donor-recipients whole blood (1–2 mL), with major ABO incompatibilities do not seem to be life-threatening. When a high dose of DLI is requested, the product may be harvested through normal or large-volume leukapheresis [38, 39]. A summary of therapeutic DLI strategies is shown in Fig. 1.

In this strategy, Wilms tumor-1 (WT1) gene expression exceeding 100 copies/10⁴ abelson murine leukemia-1 (ABL1) in bone marrow (BM) or WT-1 ≥5 copies/10⁴ ABL1 in peripheral blood, with BM in remission status (<5% blasts simultaneously with morphology and cytometry symptoms) is surrogate for starting DLI [45, 48]. In absence of GVHD for HLA identical siblings transplantation, the starting dosage is 1 × 10⁶/kg CD3+ cells and subsequently, half log increments every 30–60 days until MRD becomes negative. In unrelated transplant recipients, the initial dosage is 1 × 10⁵/kg CD3+ cells, along with half log increments every 30–60 days until MRD becomes negative. If GVHD developed after DLI, the program should be ceased until it would be completely suppressed [44‐46].

This DLI strategy has been applied in two clinical trials for ALL patients. The median time and CD3+ cell dosage after HSCT are 60–185 days and 1.5–3 × 10⁶ cells, respectively [49, 50].

This strategy might take advantage by using donor’s G-CSF-mobilized peripheral blood progenitor cells (GPBPCs) instead of their steady lymphocytes. In this method, infused cells have super anti-leukemia effects. Likewise, this approach may be accompanied by a reduction in infusion-related GVHD and also it is rarely challenged by the risk of pancytopenia [51, 52]. MRD-based modified DLI intervention is associated with transplant outcomes improvement. MRD could be evaluated using qualitative nested PCR for immunoglobulin heavy chain (IgH) VDJ, TCR gene rearrangement, WT1 expression and leukemia associated immunophenotypes (LAIP). Combination of these biomarkers is more sensitive in relapse prediction than each of WT1 or LAIP separately after transplantation [48, 51, 52]. This form of DLI is indicated after HLA-identical HSCT for patients with unfavorable cytogenetic abnormalities and also acute leukemia in more than CR1 status or in the non-remission state. Likewise, this strategy is indicated in CML in both accelerated phase (AP) and blast phase (BP) as well as myeloproliferative disorders with unfavorable cytogenetic abnormalities such as 8p11 [50‐54] (Table 1).

Short-term immunosuppressive agents (cyclosporine A or methotrexate (MTX) 10 mg/week for 2–4 weeks) are in use for prevention of DLI associated GVHD. DLI could be considered for use from days 45 to 120 after transplantation in patients without recurrence of leukemia and GVHD. In some conditions such as onset of GVHD, uncontrolled persistent infections longer than 60 days and postponement of consent, it has been suggested to avoid performing prophylactic DLI. 1 × 10⁸ MNCs/kg seems to be a proper initial cell dosage for DLI in patients who have received DLI before day 90 after transplantation. Cyclosporine A (CsA) should be continued for 2 weeks and it tapered within 4 weeks and discontinued after then if no DLI-associated GVHD occurs. In patients who received DLI after day 90 of transplantation, all immunosuppressive agents should be stopped for at least 2 weeks before DLI infusion in in order to prevent GVHD. These patients should take oral CsA or MTX 10 mg/week (single dose) for 2–4 weeks after DLI intended for prevention of DLI-associated GVHD [47, 53].

In this strategy, WT1 gene expression more than 100 copies/10⁴ ABL1 in BM or WT1 ≥5 copies/10⁴ ABL1 in peripheral blood, together with bone marrow remission (<5% blasts), and concordance of morphology and flow cytometry (FCM) is surrogate for starting DLI. Positive FCM is defined as >0.001% of cells with a leukemia-associated immunophenotypes (LAIP phenotype in ≥1 BM samples after transplantation) [48]. The immune intervention before DLI is determined as a post transplantation immune suppression which should be immediately tapered and then discontinued in patients with MRD+ ≤100 days after transplantation. Immune suppression was immediately discontinued in MRD+ patients in whom more than 100 days have been passed from their transplantation. In HLA identical siblings recipients, DLI should be started with 1 × 10⁸/kg MNC and consequently, with half log increments every 30–60 days until MRD becomes negative, in the absence of GVHD. In unrelated transplant recipients, DLI should be started with 1 × 10⁸/kg MNC and subsequently with half log increments every 30–60 days until MRD becomes negative. If GVHD develops after DLI, the program should be stopped until it resolves [48, 55]. After DLI, patients should receive immunosuppressive medications such as CsA or MTX in order to prevent GVHD. CsA is usually started at the dosage of 2.5 mg/kg/day and it must be adjusted to maintain plasma concentration of >100 ng/mL. MTX should be started at 10 mg IV on days 1, 4, 8, and continued weekly for 2–6 weeks. In patients receiving DLI from an HLA-identical related donor, GVHD prophylaxis should be received for 2–4 weeks. In patients receiving DLI from an HLA-matched unrelated or HLA-haploidentical donor, GVHD prophylaxis regimen should be prescribed for 4–6 weeks at the discretion of the well trained physicians which usually depends on patient’s GVHD status after DLI [48, 55].

This DLI strategy has been applied in three clinical trials for lymphoma, AML and MDS patients. The median time after HSCT ranged from 35 to 287 days and the median CD3+ cell dosage ranged from 1 × 10⁷ to 5.7 × 10⁷ in these studies [42, 56, 57].

G-CSF stimulated peripheral blood stem cells should be harvested through leukopheresis and DLI might be obtained from negative fraction of CD34+ hematopoietic stem cells selection. Based on many published reports, differences among last generation devices are minimum; as a result, most of cell separator devices (such as Spectraoptia^® and Fresenius Com. Tec^®) are able to collect highly enriched lymphocyte fraction with very low erythrocyte pollution and in some cases reduced platelet content. These aliquots are therefore maintained frozen until thawing to infusion [58, 59].

A summary of prophylactic/pre-emptive DLI strategies in HLA identical transplantation is shown in Fig. 2.

Booster has indication in the following situations:

PBSC donors should be stimulated with G-CSF (10 µg/kg/day for 4 days) prior to leukapheresis. Based on recent data, the median amount of CD34‏ cells is suggested to be 3.4 × 10⁶/kg for a successful leukopheresis. Also, the median infused MNCs dosage is 2.55 × 10⁸/kg with (CsA + MTX or CsA + prednisolone or CsA + MTX + prednisolone) or without immunosuppressive treatment [4, 12, 13, 66, 67]. A summary of stem cell boost (booster) strategy for poor graft function after allogeneic transplantation is shown in Fig. 4.