Stem cell collection from peripheral blood of multiple myeloma patients

Abstract

BACKGROUND

The purpose of this paper is to demonstrate a practical stem cell collection method that provides sufficient stem cells for autologous stem cell transplantation (ASCT) in multiple myeloma (MM) patients despite low peripheral CD34 (pCD34) counts and to describe the benefits of this method for MM patients with limited resources.

AIM

To demonstrate a practical method for stem cell collection.

METHODS

Stem cell collection data on the last 300 patients at a community cancer center in Washington were reviewed. We report on the methods of collection, including medications used and timing, used by the blood blank as well as their outcomes. The three MM patients with initially very low pCD34 counts all successfully underwent stem cell collection in a single trip to the transplant center for their ASCT.

RESULTS

Three patients whose pre-collection pCD34 counts were the lowest and less than 2.5 cells/μL were identified. These patients had the commonality of having multiple barriers to transportation and likely would have been able to make only one trip for the stem cell collections.

CONCLUSION

Despite particularly low pre-collection peripheral blood CD34 counts, successful autologous stem cell collection in MM patients is feasible by routinely adding plerixafor to granulocyte-colony stimulating factor on day 4 of mobilization. There is limited analysis demonstrating that sufficient stem cells for one or more transplants can be collected using this method. This practical and novel approach may benefit the high number of MM patients who face limited resources, finances, long travel times, and social support. These results are highly relevant to physicians treating similar patients.

Key Words: Multiple myeloma; Stem cell collection; Plerixafor; Peripheral CD43 count; Autologous stem cell collection

Core Tip: We are demonstrating a practical stem cell collection method that provides sufficient stem cells for autologous stem cell transplantation in multiple myeloma patients despite low peripheral CD34 (pCD34) counts and to describe the benefits of this method for patients with limited resources. We present three patients whose pre-collection pCD34 counts were less than 2.5 cells/μL and all successfully underwent stem cell collection in a single trip to the transplant center. This approach may benefit the high number of patients who face limited resources, finances, travel abilities, and social support.

INTRODUCTION

Multiple novel agents approved by the United States Food and Drug Administration over the last decade have dramatically improved the care of multiple myeloma (MM) patients[1-3]. Despite their availability, high-dose chemotherapy (HDC) followed by autologous stem cell transplantation (ASCT) remains the standard of care for many newly diagnosed MM patients who are transplant candidates[4-6]. Access to ASCT is an independent prognostic factor associated with improved long-term survival among MM patients[7].

This paper describes a new protocol for stem cell collection at Cancer Care Northwest (CCNW), a community cancer center in Spokane, Washington United States. During the earlier years of our program, like most stem cell transplant centers, we started apheresis only when the CD34 count was at least 10 cells/μL. However, patients with limited resources were unable to make another trip for repeated cycles of apheresis, so all patients who were stem cell transplant candidates underwent collection of autologous stem cells as scheduled, regardless of initial CD34 count with the usual granulocyte-colony stimulating factor (G-CSF) + plerixafor protocol which we describe in detail. Sufficient stem cells have been collected for at least one transplant, and many times enough for two or more transplants, from nearly every eligible patient supported by CCNW over the years. Similarly, some stem cell collection centers later felt comfortable collecting when cell counts were 2.5 cells/μL. Herein, we report our experience with three patients with the lowest initial peripheral CD34 counts (pCD34) of < 2.5 cells/μL in our database. The machine used was the Optia Apheresis System, manufactured by Terumo BCT, to perform a Continuous Mononuclear Cell Collection-CMNC (individual procedure settings during procedure are patient specific, based on their lab results), and the duration of the procedure averaged 5 hours. Although multiple published articles describe using plerixafor in stem cell collection, little is known regarding the minimum pCD34 count required to proceed with plerixafor administration that would result in a meaningful collection. This report describes three patients with successful stem cell collections despite very low pCD34 counts. Additionally, the ability to collect sufficient stem cells for one or multiple transplants in a single clinic visit may benefit MM patients with limited resources and healthcare access.

MATERIALS AND METHODS

Stem cell collection data on the last 300 patients at CCNW were reviewed. Patients with pre-collection pCD34 counts of < 2.5 cells/μL (an arbitrary number chosen based on our prior experience) were identified; ten such patients were found. Each patient had undergone stem cell collections despite low initial CD34 values.

At the inception of our program, stem cell collection was typically not attempted unless the pCD34 count was at least one cell/μL. Over the years, few CCNW patients have had pre-collection pCD34 counts below 0.9 cells/μL. For such patients, G-CSF was continued for one additional week before collection, or collection was postponed to a future date. We still eventually collected stem cells from every patient needing ASCT, even if multiple attempts were required.

In reviewing the last 300 patients' data in preparation for this report, we discovered one patient with a pre-collection peripheral blood CD34 count of less than 1 (0.3 cells/μL) who underwent stem cell collection due to his specific social situation. We collected 2.46 × 10⁶ CD34+ cells/kg during the initial collection week and another 2.40 × 10⁶ CD34+ cells/kg two weeks later during a second collection cycle. We mention this particular patient for data accuracy, but he was not included in our results as he did not meet the inclusion criteria of pre-collection pCD34 count of at least 1.0 cells/μL. Additional exclusion criteria were prior history of ASCT (3), non-myeloma diagnosis (2), and missing values for day 4 pCD34 count (1). Here, we report detailed data on the remaining three patients. Patients’ MM-related data were obtained from the oncology clinic charts. Daily pCD34 counts, white blood cell counts, and collected product stem cell numbers were obtained from the Spokane Vitalant Blood Center’s records. Data were de-identified before being provided to the primary researcher.

Our well-established clinical protocol for autologous stem cell collection from rural MM patients in one trip is described here and summarized in Table 1. For patients living outside the greater Spokane area, 10 μg/kg of G-CSF is administered at home or at their local hospital (depending on the insurance coverage) starting on a Friday for three mornings. Patients then travel to our center on Sunday afternoon, and CCNW arranges hotel accommodations for the duration of their stay.

Table 1 Clinical protocol for stem cell collection from rural multiple myeloma patients in one trip.

	Friday	Saturday	Sunday	Monday	Tuesday	Wednesday	Thursday	Friday
Event	Mobilization day 1	Mobilization day 2	Mobilization day 3	Mobilization day 4	Collection day 1	Collection day 2	Collection day 3	Collection day 4
AM	G-CSF	G-CSF	G-CSF	G-CSF	G-CSF	G-CSF	G-CSF	G-CSF
PM				Plerixafor	Plerixafor	Plerixafor	Plerixafor
			Arrival in town		Possible departure for home	Possible departure for home	Possible departure for home	Departure for home

G-CSF: Granulocyte-colony stimulating factor.

On Monday, following day 4 administration of G-CSF, patients undergo large-bore central venous catheter placement in preparation for Tuesday’s stem cell harvesting. Each patient, except patients with very high pCD34 counts at > 40 cells/μL, receives plerixafor 0.24 mg/kg (with dose adjustment for creatinine clearance) every evening starting on Monday (Day 4 of mobilization and the evening before the collection day 1). G-CSF is continued throughout the collection series. Depending on each collection product’s absolute quantity of CD34-positive cells, patients return home at the end of collection day 1, 2, 3, or 4.

RESULTS

Three MM patients with very low pCD34 counts (< 2.5 cells/μL) were mobilized according to our routine institutional protocol. All three patients underwent successful collections despite very low initial pCD34 counts. Two patients were later treated with HDC followed by ASCT. No unusual complications (including inadequate engraftment) were noted. Patients' individual clinical data are described below and summarized in Tables 2, 3, and 4, and aggregate clinical data are summarized in Table 5.

Table 2 Patient 1 treatment courses and response.

Patient 1 (59 M)	Monday	Tuesday	Wednesday	Thursday	Two weeks following collection
Event	Mobilization Day 4 (Day 4 GSF; pre-collection)	Collection Day 1 (Day 5 G-CSF)	Collection Day 2	Collection Day 3 (collection complete)	HDC (Melphalan 200 mg/m2)
pCD34 (cells/μL)	2.10	22.03	32.20	11.40
WBC (cells/μL)	14.60 × 103	28.70 × 103	42.10 × 103	39.50 × 103
Product cell count (CD34 cells/kg)		3.45 × 106	3.94 × 106	1.42 × 106
Total yield (CD34 cells/kg)				8.81 × 106
Infusion (CD34 cells/kg)					4.16 × 106

G-CSF: Granulocyte-colony stimulating factor; WBC: White blood cell; HDC: High-dose chemotherapy.

Table 3 Patient 2 treatment courses and response.

Patient 2 (62 F)	Monday	Tuesday	Wednesday	Thursday	Friday	Two weeks following collection
Event	Mobilization Day 4 GSF (pre-collection)	Collection Day 1 (Day 5 G-CSF)	Collection Day 2	Collection Day 3	Collection Day 4 (Collection complete)	HDC (Melphalan 200 mg/m2)
pCD34 (cells/μL)	1.30	22.03	15.70	14.00	14.10
WBC (cells/μL)	15.07 × 103	22.41 × 103	19.55 × 103	23.14 × 103	25.53 × 103
Product cell count (CD34 cells/kg)		1.79 × 106	2.67 × 106	2.76 × 106	2.40 × 106
Total yield (CD34 cells/kg)					9.62 × 106
Infusion (CD34 cells/kg)						3.12 × 106 CD34 cells/kg

G-CSF: Granulocyte-colony stimulating factor; WBC: White blood cell; HDC: High-dose chemotherapy.

Table 4 Patient 3 treatment courses and response.

Patient 3 (67 M)	Monday	Tuesday	Wednesday	Thursday
Event	Mobilization Day 4 GSF (pre-collection)	Collection Day 1 (Day 5 G-CSF)	Collection Day 2	Collection Day 3 (collection complete)
pCD34 (cells/μL)	2.30	15.50	21.20	30.20
WBC (cells/μL)	15.20 × 103	20.70 × 103	28.70 × 103	29.60 × 103
Product cell count (CD34 cells/kg)		2.23 × 106	3.39 × 106	4.96 × 106
Total yield (CD34 cells/kg)				10.58 × 106
Infusion (CD34 cells/kg)

G-CSF: Granulocyte-colony stimulating factor; WBC: White blood cell.

Table 5 Aggregate patient collection summary.

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Patient	Age	Sex	Pre-collection pCD4 count (cells/μL)	Collection day 1 pCD34 count (cells/μL)	Collection day 2 pCD34 count (cells/μL)	Collection day 3 pCD34 count (cells/μL)	Collection day 4 pCD34 count (cells/μL)	Total apheresis yield (CD34+ cells/kg)	Infusion (CD34+ cells/kg)
Patient 1	59	Male	2.10	22.03	32.20	11.40		8.81 × 106	4.16 × 106
Patient 2	62	Female	1.30	22.03	15.70	14.00	14.10	9.62 × 106	3.12 × 106
Patient 3	67	Male	2.30	15.50	21.20	30.20		10.58 × 106

Patient 1 was a 59-year-old man with past medical history of diabetes mellitus and chronic obstructive pulmonary disease who initially presented with a pathologic femur fracture and was diagnosed with MM (oligosecretory; bone marrow plasmacytosis > 50%; hyperdiploid clone; multiple lytic bone lesions; normal kidney function). For the pathologic femur fracture, he had surgery and adjuvant radiation therapy. He was enrolled in a randomized phase II clinical trial and treated with Daratumumab, Lenalidomide, Bortezomib, and Dexamethasone. Following three months of therapy, he achieved a very good partial response (VGPR). The patient lived 90 miles from CCNW and completed the out-of-town institutional protocol for stem cell collection, arriving in Spokane on a Sunday afternoon (Day 3 of G-CSF). On Monday, daily AM G-CSF was continued at 10 μg/kg, and he received plerixafor 0.24 mg/kg on Monday evening. Stem cell collection occurred Tuesday through Thursday, after which the patient returned home following a 4-night stay. Collection and infusion data are described in Table 2. Two weeks following collection, the patient received HDC (Melphalan 200 mg/m²) followed by an infusion of 4.16 × 10⁶ CD34+ cells/kg. ASCT course was uneventful. Neutrophil engraftment was performed on day +11, with platelet engraftment on day +12. The patient was then started on maintenance monthly daratumumab and low-dose lenalidomide. Patient 1 continued to be in minimal residual disease negative clinical remission (CR) 18 months following ASCT.

Patient 2 was a 62-year-old woman with past medical history of hypertension, depression/anxiety, and hypothyroidism diagnosed with MM [IgA Lambda; M spike 3.1 g/dL; Ig A 4662 mg/dL; serum lambda light chains 135.9 mg/L; bone marrow plasma cells 30%-40%; positive for t (4;14); lytic bone lesions]. She was treated with lenalidomide, bortezomib, and dexamethasone (RVD) for three months and achieved VGPR. The patient arrived at the transplant center locale on Sunday, and stem cell collection occurred from Tuesday to Friday. Collection data are described in Table 3. Despite the initially low pCD34 count of 1.3, the collection yielded a total of 9.62 × 10⁶ CD34+ cells/kg. The collection series was terminated after four days, with the patient staying in the transplant center locale for five nights. Two weeks following collection, she received HDC (Melphalan 200 mg/m²) followed by an infusion of 3.12 × 10⁶ CD34+ cells/kg. ASCT course was uneventful. Neutrophil engraftment was performed on day +11, with platelet engraftment on day +14. Day +100 restaging studies demonstrated the patient to be in stringent CR. A restaging bone marrow biopsy was not performed due to the COVID-19 pandemic. Maintenance therapy with lenalidomide and ixazomib was initiated.

Patient 3 was a 67-year-old man with past medical history of asthma, hepatitis C, hyperlipidemia, hypertension, and previous pulmonary emboli who presented with a biopsy-proven nasal plasmacytoma extending into the sinuses. Further workup revealed bone marrow plasmacytosis of 17% (abnormal hyperdiploid clone) and diffuse bone lesions on magnetic resonance imaging bone survey. The patient was diagnosed with IgG Lambda MM but was lost to follow-up for four months before therapy was initiated. Upon re-establishing care at CCNW, the patient received radiation therapy to his sinuses and was started on RVD therapy. Following four cycles of therapy, he achieved a VGPR and was considered for HDC and ASCT. During the pre-transplant workup, the patient was discovered to have chronic active hepatitis C infection. Treatment for hepatitis C initially delayed his transplant, and the transplant was later delayed once again due to pulmonary emboli. While on RVD, the patient’s disease progressed, and he was switched to carfilzomib and daratumumab. He achieved a partial response on this regimen, after which the decision was made to proceed with stem cell collection. As the patient lived 100 miles from the transplant center, the out-of-town institutional protocol was followed, with the patient arriving on a Sunday. Stem cell collection began on Tuesday (day 5 of G-CSF). Following three collection days, the total yield was 10.58 × 10⁶ CD34+ cells/kg, and the collection series was ended. Collection data are described in Table 4. The patient returned home after a four-night stay in the transplant center locale. An ASCT was planned for within a few weeks of collection. However, the patient’s clinical status acutely worsened, potentially related to his multiple medical comorbidities. The patient was never able to undergo ASCT. The patient and his family declined further therapy, and the patient expired three months following stem cell collection.

Post-transplant, patient 1 had consolidation with Daratumumab, Lenalidomide, Bortezomib, and Dexamethasone for 6 weeks followed by maintenance therapy with Darzalex and Revlimid for 3 years. Since his transplant, he has been in complete remission for nearly 7 years. Patient 2 started post-transplant maintenance therapy of lenalidomide and ixazomib, but she decided to stop after one month. She has been in complete remission for over 5 years. After patient 3 had successful stem cell collection, his multiple medical comorbidities worsened. The patient and his family declined further therapy, and the patient expired three months following stem cell collection.

DISCUSSION

In this study of rural MM patients in need of autologous stem cell collections, sufficient hematopoietic stem cells (HSCs) for one or more transplants were collected despite initially very low pCD34 counts (< 2.5 cells/μL) by routinely adding plerixafor to G-CSF on day 4 of mobilization. Plerixafor inhibits the CXCR4 chemokine receptor and blocks the binding of its cognate ligand, stromal cell-derived factor-1α (SDF-1α). Both SDF-1α and CXCR4 play a role in the trafficking and homing of human HSCs to the marrow compartment. Once in the marrow, stem cell CXCR4 assists in anchoring these cells to the marrow matrix, either directly via SDF-1α or through the induction of other adhesion molecules. It has been shown that plerixafor treatment results in elevations in circulating HSCs[8].

In December 2008, plerixafor was formally approved by the United States Food and Drug Administration for autologous transplantation in patients with non-Hodgkin’s lymphoma or MM[9]. The number of pCD34 cells has long been a guide to optimal timing for collecting HSCs. Before the availability of plerixafor, a pCD34 count ≥ 15 cells/μL was recommended before beginning collection[10]. A phase III, multicenter, randomized (1:1), double-blind, placebo-controlled study concluded that plerixafor and G-CSF resulted in a significantly higher proportion of non-Hodgkin’s lymphoma patients achieving optimal CD34+ cell target for transplantation in fewer apheresis days as compared to G-CSF treatment alone[11].

Another phase 3, multicenter, randomized (1:1), double-blind, placebo-controlled study evaluated the safety and efficacy of plerixafor with G-CSF in mobilizing HSCs in patients with MM. This study concluded that plerixafor and G-CSF were well tolerated, and significantly more patients collected the optimal CD34+ cell/kg target for transplantation earlier than patients treated with G-CSF alone. They did not report the pre-collection (mobilization day 4) pCD34 counts[12]. A long-term follow-up for these two studies showed that the use of plerixafor plus G-CSF does not have a negative outcome on overall survival and progression-free survival at five years in these patients with non-Hodgkin lymphoma or MM[13].

Despite the proven benefits of adding plerixafor to G-CSF for collecting stem cells from MM patients, this technique has yet to be routinely adopted by institutions on a wide scale. Some suggest using plerixafor in patients with MM whose G-CSF day 4 pCD34 count is < 40 cells/μL[14]. Others recommend the "on demand" use of plerixafor[15]. Micallef et al[16] used a risk-adapted algorithm and recommended adding plerixafor to G-CSF if pCD34 count on day 4 or 5 was < 10/μL. In addition, they suggested adding plerixafor if, on any day, the daily collection yield was < 0.5 × 10⁶ CD34/kg. Cooper et al[17] described 277 consecutive MM and lymphoma patients who underwent stem cell collection. Plerixafor was used in 41.5% of patients. Patients who required "rescue" plerixafor had a median peripheral blood CD34 count of 9 (1-19) on day 4 (pre-collection) lab check. Their publication provides no further details about patients with very low pre-collection pCD34 counts. Our literature review did not identify any published data regarding the minimum CD34 count required to proceed with plerixafor administration that would then result in a meaningful collection. Our report is the first to demonstrate the feasibility of successful stem cell collection from patients with very low pCD34 counts.

Although the use of HDC followed by ASCT improves overall survival of patients with MM, many patients experience significant challenges in attaining medical care. Rural and underserved populations face higher rates of cancer incidence and mortality, yet specialized oncologic care is often sparse in these communities. These patients may also have difficulties accessing transportation to distant cancer centers, resulting in delayed time to diagnosis or no access to necessary care. Furthermore, these populations experience the additional burden of lower levels of health literacy[18,19]. Oftentimes, these patients may be turned away due to low pCD34 counts, and due to various social and transportation barriers, they may then be unable to return for repeat collection attempts. Our proposed method of collecting stem cells on day 4 of mobilization from patients with very low initial pCD34 counts may alleviate some of these challenges.

Additionally, Plerixafor can be a more expensive regimen. It was covered by insurance for our patients, avoiding adding financial toxicity to the patients we reported on, but it may be a consideration for other healthcare systems. Otherwise, collection of the stem cells at lower levels decreases other areas of financial burden related to transportation, housing, and co-payments for additional visits, particularly for patients in resource-limited settings. We do not have comparisons with other regimens. However, other regimens such as G-CSF alone or chemotherapy-based mobilizations may offer different or better outcomes and should be explored in future research as well.

A limitation of our study is the small sample size of patients. A larger data set would allow broader application and generalizability of this method. With this brief report, we aim to encourage other transplant centers to initiate collection in similar patients with very low pCD34 counts, especially those who live far from the center.

CONCLUSION

Successful autologous stem cell collection for one or more transplants is feasible in MM patients with very low pre-collection peripheral blood pCD34 counts (< 2.5 cells/μL) by routinely adding plerixafor to G-CSF on day 4 of mobilization. There is limited analysis demonstrating success with this technique. Considering that many MM patients requiring stem cell transplantation face social and transportation barriers to care, our method may ease these barriers by allowing centers to collect sufficient stem cells in a single trip to the transplant center. Our practical approach and novel results are highly relevant to physicians treating similar patient populations. We also encourage future research into this subject for better understanding.