Combined positive and negative cell selection from allogeneic peripheral blood progenitor cells (PBPC) by use of immunomagnetic methods

A novel high throughput immunomagnetic cell sorting system for potential clinical scale depletion of T cells for allogeneic stem cell transplantation

OBJECTIVE

To develop an immunomagnetic cell separation system for allogeneic hematopoietic stem cell (HSC) transplantations, which can achieve a high level of T-cell depletion (at least 4.0 log(10)), high level of recovery of hematopoietic stem cells (>90%), with a high throughput (>10(6) cells/second).

METHODS

Peripheral blood leukocytes (PBLs) from buffy coats were spiked with CD34-expressing cells (KG1a) to mimic a leukaphoresis product containing stimulated HSCs. T cells were labeled with anti-CD3(+) Dynabeads and separated in a quadrupole magnetic cell sorter (QMS). The performance of the system with respect to T-cell depletion and recovery of non-T cells and spiked KG1a was determined using four-color, flow cytometry analysis, with the aid of Trucount cell-concentration calibration beads. Limiting dilution assays were also performed to quantify the log(10) depletion of clonable T cells.

RESULTS

While the general performance of the QMS system is governed by proven theoretical principles, significant system variability exist, not all of which can be explained by our current understanding. Consequently, a factorial design was employed, guided by JMP software, to optimize the labeling conditions and operation of the QMS focused on maximizing the depletion of T cell, and recovery of unlabeled cells including KG1a cells. From these studies, an optimized, no wash, immunomagnetic labeling protocol and optimized QMS operating conditions were developed. For an average initial cell concentration of 1.7 x 10(8) total cells, an average 3.96 +/- 0.33 log(10) depletion (range, 3.53-4.34) of CD3(+)CD45(+) cells with a mean 99.43% +/- 4.23% recovery of CD34(+)CD45(+) cells (range, 94.38-104.90%) was achieved at a sorting speed of 10(6) cells/s (n = 6). Limiting dilution assays on the T-cell depleted fractions, which gave a log(10) depletion of 3.51 for the clonable T cells.

CONCLUSION

We suggest that this system will provide superior performance with respect to T-cell depletion and CD34(+) recovery for clinical allogeneic bone marrow transplants. Ongoing studies, on a clinical scale, are being conducted to demonstrate this claim.

Methods in cell separations

Research in the field of cell biology and biomedicine relies on technologies that fractionate cell populations and isolate rare cell types to high purity. A brief overview of methods and commercially available products currently used in cell separations is presented. Cell fractionation by size and density and highly selective affinity-based technologies such as affinity chromatography, fluorescence-activated cell sorting (FACS) and magnetic cell sorting are discussed in terms of throughput, yield, and purity.

Comparison of two immunomagnetic separation technologies to deplete T cells from human blood samples

The objective of this study was to compare the performance of two immunomagnetic separation technologies to deplete T cells from buffy coats of human blood. Specifically, two versions of the commercial MACS(R) Technology: MiniMACS and SuperMACS, and a prototype, flow-through system, the QMS, were evaluated. Peripheral blood mononuclear leukocytes (PBL) were isolated from buffy coats and an immunomagnetic separation of CD3(+) cells was conducted using company and optimized labeling protocols. To mimic peripheral blood containing bone marrow purged hematopoietic stem cells, HSC, CD34 expressing-cells (KG1a) were spiked into PBL prior to T-cell depletion once optimized depletion conditions were determined. Once the labeling protocol was optimized, the MiniMACS system performed well by producing a highly enriched CD3(+) fraction, and a respectable level of depletion of T cells and recovery of KG1a cells in the depleted fraction; an average log(10) depletion of T cells of 2.88 +/- 0.17 and an average recovery of the KG1a cells of 60.8 +/- 5.94% (n = 14). The performance of the SuperMACS system was very similar with an average log(10) depletion of T cells of 2.89 +/- 0.22 and an average recovery of KG1a of 63.1 +/- 8.55% (n = 10). In contrast, the QMS system produced an average log(10) depletion of T cells of 3.98 +/- 0.33 (n = 16) with a corresponding average recovery of 57.9 +/- 16.6% of the spiked CD34+ cells. The aforementioned QMS performance values were obtained using sorting speeds ranging from 2.5 x 10(4) to 1.7 x 10(5) cells per second. It is suggested that the lack of a 100% recovery of the unlabeled KG1a cells is the result of a previously reported "drafting" phenomena which pulls unlabeled cells in the direction of the magnetically labeled cells thereby resulting in loss of the unlabeled cells.

The beneficial role of inhibitory KIR genes of HLA class I NK epitopes in haploidentically mismatched stem cell allografts may be masked by residual donor-alloreactive T cells causing GVHD

HLA allele mismatches will provoke T-cell alloreactivity after allogeneic stem cell transplantation. As donors and recipients are usually HLA matched, the public HLA epitopes that are recognized by natural killer (NK) cells (NK epitopes) are rarely mismatched, and therefore there is rarely potential for NK alloreactivity arising from the absence of ligands for inhibitory killer immunoglobulin-like receptors (KIR). Transplants using related donors sharing only one haplotype (haploidentical donors) represent a setting in which NK epitopes are often mismatched, thus resulting in the potential for NK alloreactivity. We have analyzed engraftment, acute graft vs host disease (GVHD), leukemia relapse, and survival in 62 haploidentical transplants in relationship with potential NK alloreactivity, inhibitory, and activating KIR genes of class I HLA NK epitopes. Potential NK alloreactivity in the rejection direction was not associated with any outcome variable. Potential NK alloreactivity in the GVHD direction was associated with an increased incidence of severe GVHD and poorer patient survival but not with non-engraftment nor leukemia relapse. A higher number of activating KIR receptors in the genome of the donor was associated with a higher prevalence of GVHD. These results suggest that lack of extensive T-cell depletion in haploidentical transplantation is associated with high GVHD rates and diminishes the benefits of NK-cell alloreactivity.

Influence of platelet count and activity on thromboelastography parameters

It has been suggested that thromboelastography TEG) can help in limiting or directing the appropriate use of blood products during surgery. However, the contribution of platelets to the TEG profile has not been studied in detail. Blood was taken from eight healthy subjects and eight patients with peripheral arterial disease (PAD). Immunomagnetic separation was achieved by the addition of Dynabeads labeled with a CD41 murine antibody (to the GPIIb/IIIa receptor) to achieve 90-100% depletion of platelets from blood. This was then titrated with whole blood to achieve platelet counts of approximately 0, 25 and 50% of the original count to compare with whole blood using TEG. Platelet function was also assessed by spontaneous platelet aggregometry (SPA) at baseline and at the 50% dilution. SPA, maximum amplitude (MA) and K time were significantly different in PAD patients compared to controls (P < 0.05). In both controls and PAD patients there was a strong linear correlation between Log10 [platelet count] and MA (r = 0.97 for controls, r = 0.89 for PAD) and K time (r = -0.86 for controls, r = -0.68 for PAD). Correlation between Log10 [platelet count] and R time was poor in both groups. The MA and K TEG parameters may be most useful for assessing platelet transfusion requirements.

Combined isolation of CD34+ progenitor cells and reduction of B cells from peripheral blood by use of immunomagnetic methods

BACKGROUND

Malignant cells may contribute to relapse after autologous hematopoietic cell transplantation The effectiveness of a double immunomagnetic purging strategy combining CD34-positive with B-negative cell selection to purge peripheral blood progenitor cells (PBPCs) from patients with chronic lymphoproliferative disorders has been analyzed.

STUDY DESIGN AND METHODS

Twenty-two CD34+ cell selections from patients with follicular lymphoma (n = 14), chronic lymphocytic leukemia (n = 6), mantle cell lymphoma (n = 1), and splenic marginal zone lymphoma (n = 1) were performed by use of a magnetic cell selector followed by a negative cell selection step with anti-CD19 monoclonal antibody bound to immunomagnetic beads.

RESULTS

The PBPC components contained median CD34+ cells of 1.24 percent (range, 0.38-3.92%) and CD19+ cells of 1.83 percent (range, 0.06-69.7%). After positive selection (n = 22), 49 percent (range, 16-72%) of CD34+ cells were recovered with a purity of 93 percent (range, 24-99%). The double-positive and -negative selections (n = 20) yielded 57.5 percent of CD34+ cells (range, 33.4-79.4%) with a purity of 95 percent (range, 63-99%). Logarithms of B-cell reduction in the CD34+-cell-enriched B-cell-depleted component had a median value of 3.63 (range, 2.74-4.84 log) and CD19+ and CD5+ cells for chronic lymphocytic leukemia patients with more than 4.56 log (>3.6-5.6 log). Of 13 PBPC components that had a tumor-specific clonal signal, 10 became PCR negative after the double-selection procedure.

CONCLUSION

Combined positive and negative magnetic cell selection achieves a high grade of tumor cell reduction with up to 77 percent of the grafts being negative for tumor-specific clonal signal by PCR analysis. This technique preserves an adequate recovery of progenitor cells able to engraft.