Forbes and Fifth

Contamination of Preservation Solution in Pancreatic Islet Cell Product Transplantation

Introduction

Chronic Pancreatitis (CP) is a disease that results in the persistent inflammation of the pancreas. Digestive enzymes made by the pancreas are usually released in an inactivated form, but in patients with CP, these digestive enzymes are active and effectively digest parts of the pancreas, leading to inflammation. CP is associated with debilitating pain and low quality of life, prompting the use of surgery to reduce painful symptoms. Total pancreatectomy with clinical autotransplantation or allotransplantation of islet cells is a common treatment method for cases of moderate to severe CP (Johnson, 2014). During autotransplantation cases, the pancreas is removed and islet cells are harvested. The harvested pancreas is typically placed in chilled University of Wisconsin Solution (UWS) for transport, until islet cells can be isolated and transplanted. After isolating and washing the islet cells, a final transplant solution is prepared for hepatic portal vein infusion (Berger, 2016).

Similarly, pancreata are harvested from deceased donors and transported in chilled, balanced electrolyte solution (typically UWS) during allotransplantation. Islets are harvested from the pancreata and purified via automated or manual processes. The isolated islet cells are then prepared for transplantation onto the liver, typically through portal vein infusion (Bucher, 2005 & Gala-Lopez, 2013).

Microbiological contaminants have been shown to be present in both transport and transplant solution media. This raises questions over how safe transplanting contaminated cell products really is. Particularly during autologous procedures, prior pancreatic intervention coupled with contamination from gut lining bacteria that occurs during the excision of the pancreas can result in contaminated transport media. Since islet cells are isolated and washed but not completely purified during autotransplantation, final transplant solutions can be contaminated as well. Allotransplantation of contaminated transplant solutions has also been documented in the literature, despite purification of harvested pancreata. Even with incidences of microbiological contamination, islet transplantation procedures continue to be used to treat chronic pancreatitis and diabetes (Johnson, 2014, Berger, 2016, Bucher, 2005, & Gala-Lopez, 2013).

The role of microbiological contamination of final transplant solutions during autotransplantation and allotransplantation of islet cells has been examined through several studies in the literature (Johnson, 2014, Berger, 2016, Bucher, 2005, Gala-Lopez, 2013, Wray, 2005, Balzano, 2013, Colling, 2015, Lakey, 1995, Carrol, 1992, & Murray, 2014). However, the rate of infectious complications, incidence of concordant infections, and the most common contaminants have not been analyzed and compared between autotransplantation and allotransplantation.

A literature review was conducted to compare transport and transplant solution contamination between autotransplantation and allotransplantation procedures, as well as to make recommendations for standards of practice and future studies. Infectious complications arising from microbiological contamination were also assessed between the two categories of transplantation. The procedure through which articles were selected for the literature review is depicted in Figure 1.

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Figure 1. Article Selection Process

Materials & Methods

Literature Review Process:

A literature review was conducted using the PubMed database. Studies published from January 1900 to July 2017 were searched using the following filters: ‘microbial contamination pancreatic islet’ OR ‘pancreatic transport solution contamination’ OR ‘autologous pancreatic islet transplant’. Abstracts were initially reviewed for content and full-text articles were subsequently reviewed for relevance.

Studies including retrospective analysis, prospective analysis, or surveillance of the microbiological environment with regard to autotransplantation or allotransplantation of islet cells were included. Data regarding microbial contamination of the transport or transplant solution were required for all included studies. Studies involving dogs and lacking contamination data for transport or transplant solution were excluded from the review (See Figure 1). All studies in the final review used human pancreata for transplantation.

Following the selection of articles, studies were assessed for bias to remove noticeably subjective influences on data. Data regarding contamination of the microbiological environment, postoperative infection rates, and common contaminants were assessed in this literature review. The primary outcome was assessing the relationship between contaminated transport or transplant solution and infectious patient outcomes postoperatively. Secondary outcomes included noting common contaminants present in islet solutions, common infectious outcomes, and antibiotic administration.

Results:

A total of 697 articles from January 1900 to July 2017 were found through the search. After excluding studies pertaining to dogs and unrelated to islet transplantation, 516 studies were assessed for review eligibility. Quality of methodology, microbial contamination data, and relevance were critiqued in the remaining studies and were factors in the assessment for eligibility. After removing duplications, the selection process yielded 13 studies that met all inclusion criteria and thus are included in this review.

Table 1. Summary of Study Characteristics.

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Key: HIIA = Human Islet Isolation for Allotransplantation, HIPA = Human Islet Preparation for Allotransplantation, DHIPA = Decontamination of Human Islet Preparation for Allotransplantation.

In all 13 studies, islet cells were harvested from pancreata and placed into transport solution, typically UWS or some other balanced electrolyte solution. All but three studies provided transport solution contamination data, as samples were taken from transport solution and cultured as part of microbiologic surveillance. This procedure involves taking a small sample of islet transport solution, culturing it in a petri dish with agar and sugar, and leaving it alone for several days. If bacteria are present in the sample, several colonies will be visible on the plate after a few days. A similar procedure is also typically used when determining transplant solution contamination, except the sample is taken from the solution that will be transplanted.

Contamination in transport solution was common, ranging from 17.8% to 89.3% of cultured samples showing bacterial or fungal growth during the culture period (Table 2). Microorganisms found in transport solution were diverse across all study groups, including aerobic, anaerobic, and fungal species. A single contaminant was most commonly found in a contaminated culture. However, nearly all authors also reported multiple transport cultures with more than one microorganism present.

The most common contaminants reported in transport solution were Gram-positive aerobic bacteria (Table 2). Gram-negative species were also reported in transport solution along with anaerobic bacteria, but Gram-positive species were often also present in the culture. Here, Gram-positive and negative refers to the Gram staining procedure, during which a special purple dye is added to a culture of bacterial cells. The dye will cross the bacterial membrane and wind up in the cytoplasm and in the space between cells. Bacterial cells with thick cell walls usually contain peptidoglycan, a molecule with both sugar and protein residues. The dye will cross the membrane of these bacteria and remain stuck inside due to the thick cell walls, staining these cells purple, or Gram-positive. Bacteria with thin cell walls will allow dye to cross the membrane in both directions, often leaving a lighter pink color inside the cell. These bacteria are referred to as Gram-negative species. Staphylococcus, Streptococcus, and Candida species were particularly common among all studies in transport solution and all are Gram-positive species.

Table 2. Transport and Transplant Solution Contamination Rates

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Note: *F = Filtrate, S = Supernatant. The study by Murray et al. reported contamination in both components following centrifugation. These cases have been considered distinctly above.

After islet cells are harvested, the cells are isolated and processed prior to transplant. In the case of allotransplantation, an accompanying purification process occurs using an antibiotic wash as a decontaminating agent. Cefazolin is the standard antibiotic used during this procedure, but the study by Qi et al. presented a novel decontamination method using multiple antibiotics in tandem to purify contaminated islet cells. This study reported low contamination rates following the special purification process.

Final transplant solution, containing the processed islet cells that are to be infused via the hepatic portal vein, was also studied as part of microbiological surveillance. This is the solution that was directly transplanted into patients with CP, so it is carefully monitored for bacterial contamination. Contamination of the final islet product also occurred, but at a lower rate than transport solution. Final transplant contamination ranged from 4.3% to 64.3% of cultured samples. Fungal and bacterial growth were reported in final transplant solution, with Gram-positive aerobic bacteria being the most common contaminants. Fungal species were rarely reported but are of special concern since treatment of individuals with fungal organisms is different from treatment of individuals with bacterial infections. Staphylococcus and Streptococcus species were common, but studies reported greater frequencies of Enterococcus and various other Gram-positive species in final islet preparations relative to the original, unpurified transport solutions (Table 2).

Despite the lack of purification procedures during typical autotransplantations, contamination of final transplant solution saw a percent decrease ranging from 10.4% to 37.1%. Harvesting of donor pancreata for allotransplantation includes a decontamination procedure with antibiotics. Contamination of final transplant solution was markedly reduced in these cases, with studies reporting decreases of 13.5% to 51.8% in sterility cultures. It is generally believed that these decreases are due to the use of antibiotics during the purification process.

Infectious complications occurred in nearly all study groups, both from autotransplantation and allotransplantation. On average, approximately 21% of patients experienced infectious complications postoperatively, ranging from minor cold-like infections to pneumonia. However, infections resulting from concordant organisms—when reported—typically comprised less than 10% of the study population. Concordant organisms are defined as being present in transplant solution as well as the direct causal agents of postoperative infection. A comprehensive description of each study’s infectious complications rates, along with the most common infection and the degree of concordance (if indicated) is presented in Table 3. Antibiotic coverage was provided prophylactically and usually consisted of Cefazolin or Clindamycin (Table 3).

Table 3. Infectious Complications Summary and Concordance

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Note: 1. Most commonly caused by Staphylococcus epidermis and found to be 16.6% concordant. 2. Caused by mixed Gram-positive and Gram-negative species with 14.3% concordance to transplant solution.

Discussion

The results of this review show that despite contamination of final transplant solution, post-operative infectious complications tend to be minimal. However, there is a lack of data in the literature with regard to concordance of disease, as most studies do not directly analyze the relationship between transplant contaminants and postoperative infectious agents. Studying concordance and disease subtyping in greater detail would allow for a more comprehensive determination of the role of microbiological contaminants in transplant solution. Most of the literature supports that the main source of microbiological contamination is endogenous gut bacteria, but there have been documented instances of bacteria being present in transport solution that were not from the patient. Determining concordance would thus, help separate cases of microbial contamination from endogenous bacteria, present from prior pancreatic intervention, from newly introduced bacteria that developed by some other means. In other words, if postoperative infections are indeed most often caused by transplant solution contamination, then this would need to be monitored to a greater degree. However, if the transplant solution contaminants and postoperative infectious agents do not match, then the cause of postoperative infection may be found elsewhere.

Gram-positive aerobic species were most commonly found in the microbiological environment, which aligns with the general belief that contamination arises from intestinal bacteria that is perturbed during the harvesting procedure (Jolissaint, 2016). Also, it was common for each transport or transplant culture to be contaminated with one organism. However, several cultures across multiple studies presented multiple organisms in solution. Despite the presence of multiple contaminants in transplant product, studies did not report greater rates of infection in patients receiving these islet cells (Johnson, 2014, Berger, 2016, Bucher, 2005, & Gala-Lopez, 2013, & Jolissaint, 2016). Although, most transplant solutions did not contain multiple, distinct organisms, thus the limited cases observed in the studies are likely unrepresentative of a large enough sample to draw conclusions from.  

The use of antibiotics as a decontamination protocol was typically not discussed by most of the studies. Although, the norm is to purify donor islet cells with Cefazolin during allotransplantation. A study by Qi et al. (2016) proposed a novel method of decontamination: using two or more antibiotics in tandem during the purification process (Qi, 2016). The study showed that this method is fast, affordable, and reliable in reducing microbiological contamination. An overarching trend was that allotransplant products saw a marked reduction in microbiological contamination from transport to transplant solution, as compared to autotransplant products. The main difference between the two procedures is the origin of the harvested islet cells. Since pancreata are harvested from donors during allotransplantation, more extensive purification procedures are carried out to prevent adverse reactions in the patient who receives the pancreas.  Many of the autotransplant studies did not discuss a purification procedure, as the islet cells were often simply isolated, processed, and transplanted without decontamination. It is recommended that decontamination procedures to purify islet cell products should be studied to gain further insight into the role of purification on reducing the risk of infectious complications from microbiological contamination (Qi, 2016).

Another common trend among the studies of this review was a lack of data regarding antibiotic treatment plans used to follow up with patients postoperatively. There seems to be no consensus on whether patients who received contaminated transplant products should receive antibiotics immediately or only after presenting with an infection. One study by Gala-Lopez et al. (2013) provided an extensive summary of postoperative interventions used to monitor infections and patient recovery (Gala-Lopez, 2013). All patients who received contaminated transplant products received antibiotics immediately, which are prescribed specific to patient allergies and the contaminants identified in culture. C-Peptide tests and imaging were also used postoperatively to corroborate manifestation of clinical infection. The study reported zero infectious complications, which may be a result of this extensive postoperative care plan (Gala-Lopez, 2013). Further studies that track postoperative treatment, particularly those using specific treatment and imaging to determine infections or complications, are recommended to develop new standards of practice.

The microbiome, which is comprised of all the microorganisms in the body, could potentially be of great importance to future microbiological contamination studies. Thus far, the literature supports that contamination of the microbiological environment should not preclude autotransplantation, particularly with regard to treatment of chronic pancreatitis or diabetes. However, there is a lack of data supporting the claim that patients who receive self-contaminated autotransplant products have a lower risk of infection than those that are newly introduced to transplant contaminants. Further research is necessary, particularly in relation to concordance and subtyping as previously mentioned, to determine the role of the microbiome in regulating responses to transplanted contaminants.

Several studies have assessed the role of transplant solution or organ preservation solution in the kidneys and liver, both of which have implications for islet transplantation (Ruiz, 2009, Veroux, 2010, Botterel, 2010, Chaim, 2011, Brown, 2012, & Rodrigues, 2013). A study by Ruiz et al. (2009) reported high levels of contaminated liver preservation solution for transplantation (Ruiz, 2009). Though contamination of pre-transplant solution was high, most patients did not experience clinical infections related to the contaminants when prophylactic antibiotics were administered (Ruiz, 2009). Veroux et al. (2010) reported similar findings in contaminated kidney preservation fluid, with prophylactic antibiotic administration believed to be linked with prevention of the clinical manifestation of infectious symptoms post-transplantation (Veroux, 2010).

Sources of contamination outside the patient should also be investigated and monitored as a quality control measure. This would help shed light on other sources of contamination that are unrelated to contaminants in the transplant products themselves. Several studies included in this review monitored automated processing and manual processing of islet cells, along with the microbiological environment, in order to prevent the introduction of contaminants from the external environment. The sterility of procedures used to harvest donor pancreata was also an important consideration in the allotransplantation studies. This was done in the hopes that careful monitoring and standardization of technique can reduce the rate of contaminated transplant products. Automation of processing is recommended for all procedures, as it standardizes the mechanism, while simultaneously reducing variability in procedure.

Conclusion

Autotransplantation and allotransplantation are viable treatment options for patients experiencing distress due to chronic pancreatitis and diabetes. Both procedures require the transplantation of islet cells, either from the patient or a donor. Contamination of the microbiological environment, in both transport and transplant solution, has been well documented in regard to both procedures. Despite moderately high rates of microbiological contamination in transplant solution, postoperative infectious complications appear to remain uncommon. Future studies geared toward the role of antibiotics in postoperative care will help improve the current understanding of postoperative infectious outcomes. Perhaps many of the current infectious outcomes plaguing patients could be avoided altogether based on administration of specific antibiotics immediately following procedures. The microbiome of the patient should also be studied in greater detail, along with concordance and subtyping of contaminants, to generate a more specific and encompassing profile of the microbiological environment as it pertains to human islet transplantation.


References

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Acknowledgements

Special thanks to Dr. Horacio Rilo, my mentor throughout this study, who advised me during the literature search and provided an unpublished study of his to include, as well. This study was completed through the Pancreas Disease Center, affiliated with the Northwell Health System in Manhasset, NY.

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Volume 12, Spring 2018