Reimmunization and splenic autotransplantation: a long-term study of immunologic response and survival following pneumococcal challenge

Splenic auto-transplantation after splenectomy for trauma: evaluation of a new technique

BACKGROUND

Splenic autotransplantation is a promising method to recover splenic functions after traumatic splenectomy. However, it is associated with several postoperative complications, such as subphrenic abscess, intestinal obstruction and torsion of the omentum with necrosis of the implanted splenic tissues. Therefore, the aim of this study is to evaluate a new splenic autotransplantation technique that could overcome those complications.

MATERIALS AND METHODS

A single segment of the spleen was implanted inside a pedunculated omental pouch and fixed in the native site of the spleen in 15 patients who underwent splenectomy for abdominal trauma. This group of patients was compared with the next 17 patients who underwent splenectomy alone. Additionally, splenic functions of the patient and control groups were evaluated 3 months using peripheral blood smear [the presence of Howell-Jolly (HJ) bodies] and abdominal contrast-enhanced computed tomography (CECT).

RESULTS

All patients who underwent splenic autotransplantation showed evidence of a well-vascularised splenic tissue on CECT and normal peripheral blood smear without HJ bodies 3 months postoperatively. No postoperative complications related to splenic autotransplantation were observed, and platelet count after 3 months was significantly higher in patients who underwent splenectomy only (p = 0.04).

CONCLUSIONS

Splenic autotransplantation using the aforementioned technique could restore splenic functions with minimum postoperative complications related to the procedure.

Spleen autotransplantation provides restoration of functional splenic lymphoid compartments and improves the humoral immune response to pneumococcal polysaccharide vaccine

After splenectomy, patients have an increased risk of overwhelming post-splenectomy infection (OPSI) or sepsis involving encapsulated bacteria such as pneumococcus. The value of spleen autotransplantation after splenectomy because of trauma has long been questioned. Much attention has been given to the restoration of mononuclear phagocyte system (MPS) function, which appeared to be similar to that of splenectomized individuals. The presence of specific anti-pneumococcal antibodies may enhance phagocytosis of opsonized bacteria by other parts of the MPS, as present in the liver. Therefore, in the present study we have evaluated the restoration of the humoral immune response after spleen autotransplantation, especially to pneumococcal capsular polysaccharides (PPS). Wistar rats were divided into three groups which were operated as follows: splenectomy, splenectomy followed by autotransplantation, and sham operation. After 12 weeks the rats were vaccinated with 23-valent pneumococcal vaccine. Blood samples were taken after 3 days, 3 and 6 weeks for anti-PPS IgM and IgG ELISA against types 3, 4, 6, 9, 14 and 23. In addition, immunohistological studies were performed on the autotransplants. Significant antibody titre rises were found in a main proportion of the autotransplanted rats, comparable to sham-operated rats. Splenectomized rats showed as well a significantly lower increase in immunoglobulin levels, as significant differences in the proportion of rats showing a minimum two-fold increase of antibody level, considered to represent an adequate response. The titres were highest 3 days after vaccination. Immunohistochemical studies demonstrated structurally functional autotransplants, including an intact marginal zone. Considering this significant anti- pneumococcal antibody response, spleen autotransplants can be expected to enable an improved humoral response to PPS, and to contribute to protection against OPSI after splenectomy.

Immune response capacity after human splenic autotransplantation: restoration of response to individual pneumococcal vaccine subtypes

OBJECTIVE

To evaluate features of general immune function, in particular the restoration of the humoral immune response to pneumococcal capsular polysaccharides, in humans undergoing a spleen autotransplantation after splenectomy because of trauma.

SUMMARY BACKGROUND DATA

After splenectomy, patients have an increased risk of overwhelming infection or sepsis involving encapsulated bacteria such as pneumococci. The value of human spleen autotransplantation after splenectomy because of trauma has long been questioned. Mononuclear phagocyte system function appeared to be similar to that in splenectomized persons. The presence of specific antipneumococcal antibodies would allow other parts of the mononuclear phagocyte system, such as those in the liver, to phagocytose opsonized bacteria.

METHODS

Ten consecutive patients undergoing splenectomy followed by autotransplantation were compared with the next 14 consecutive patients undergoing splenectomy alone. After a minimum of 6 months, the patients were vaccinated with 23-valent pneumococcal vaccine. Blood samples were taken at the time of vaccination and after 3 and 6 weeks for antipneumococcal capsular polysaccharides IgM and IgG enzyme-linked immunosorbent assay against types 3, 4, 6, 9, 14, and 23. Splenic regrowth was evaluated by scintigraphy.

RESULTS

Surprisingly, several of the nonautotransplanted patients showed scintigraphic activity, indicating the presence of either accessory spleens or traumatic seeding (splenosis). Significant antibody titer increases (more than twofold) were found for both IgM and IgG in the autotransplanted patients. Splenectomized-only patients showed no significant increase in Ig levels in patients without splenic regrowth and partial improvement in patients with splenosis/accessory spleens.

CONCLUSIONS

Considering this significant antipneumococcal antibody increase, spleen autotransplants can be expected to permit an adequate humoral response to pneumococcal infections and presumably also to other TI-2 antigens, and to protect against overwhelming postsplenectomy infection or sepsis.

Fc-receptor function after human splenic autotransplantation

Mononuclear phagocytic function was studied using the Fc-receptor test in 24 patients who underwent splenectomy, ten of whom underwent splenic autotransplantation. All patients undergoing autotransplantation had mononuclear phagocyte system (MPS) activity at the transplantation sites. In eight of the 14 patients who did not undergo autotransplantation there was also scintigraphic MPS activity indicative of ectopic splenic tissue. Although the Fc-receptor test showed delayed and monoexponential blood clearance in all patients after splenectomy, there were no significant differences between the patient groups. Autotransplantation of small amounts of splenic tissue after splenectomy provides some MPS activity but is inadequate for blood clearance.

Autologous splenic transplantation for splenic trauma

OBJECTIVE

The authors reviewed the experimental evidence, surgical technique, complications, and results of clinical trials evaluating the role of autologous splenic transplantation for splenic trauma.

SUMMARY BACKGROUND DATA

Splenorrhaphy and nonoperative management of splenic injuries have now become routine aspects in the management of splenic trauma. Unfortunately, not all splenic injuries are readily amenable to conventional spleen-conserving approaches. Heterotopic splenic autotransplantation has been advocated for patients with severe grade IV and V injuries that would otherwise mandate splenectomy. For this subset of patients, splenic salvage by autotransplantation would theoretically preserve the critical role the spleen plays in the host's defense against infection.

METHODS

The relevant literature relating to experimental or clinical aspects of splenic autotransplantation was identified and reviewed. Data are presented on the experimental evaluation of autogenous splenic transplantation, methods and complications of autotransplantation, choice of anatomic site and autograft size, and results of clinical trials in humans.

RESULTS

The most commonly used technique of autotransplantation in humans involves implanting tissue homogenates or sections of splenic parenchyma into pouches created in the gastrocolic omentum. Most authors have observed evidence of splenic function with normalization of postsplenectomy thrombocytosis, immunoglobulin M levels, and peripheral blood smears. Some degree of immune function of transplanted grafts has been demonstrated with in vivo assays, but the full extent of immunoprotection provided by human splenic autotransplants is currently unknown.

CONCLUSIONS

Multiple human and animal studies have established that splenic autotransplantation is a relatively safe and easily performed procedure that results in the return of some hematologic and immunologic parameters to baseline levels. Some aspects of reticuloendothelial function are also preserved. Whether this translates into a real reduction in the morbidity or mortality rates from overwhelming bacterial infection is unknown and requires further investigation.

The vascular supply of splenic autotransplants

The close opposition of blood to phagocytic cells lining the pulp cords and marginal sinus has been proposed as a contributing factor in the clearance mechanism of the spleen. The vasculature of splenic autotransplants was investigated in rats using microcorrosion casts. Six-month-old splenic autotransplants and unoperated control spleens were selectively perfused and a methyl methacrylate cast was made. Scanning electron microscopy of these corroded casts was performed. In autotransplants, the marginal zone capillary network was abnormal with the fine network of capillaries replaced by dilated blood vessels. The red pulp cords were also found to be abnormal with increased diameter and loss of the fine saccular dilations found in normal spleens. The abnormally dilated capillaries and cords in the autotransplants may decrease antigen contact with these cells and hence explain previous reports of reduced phagocytic function.

Regeneration of autotransplanted splenic tissue at different implantation sites

Inbred animals (Lewis rats) were used to investigate the regeneration of autologously implanted splenic tissue at intra-omental and subcutaneous sites. Quantitative immunohistology with monoclonal antibodies against lymphocytes and macrophages was performed to analyse the cell density of red pulp (RP), periarteriolar lymphoid sheath (PALS), marginal zone (MZ) and follicle, 7-180 days after transplantation. Antigenic, allogeneic and mitogenic stimulation and Northern blotting were also performed. Transplant groups differed from spleen only in the reduced size of PALS; however, quantitative analysis demonstrated subtle differences between spleen and transplants. The cell density of B-cells and ED-1+ macrophages was reduced in the RP, Tsupp/cyt-cells were decreased and B-cells increased in PALS, and B-cells and Thelper-cells reduced in the MZ. No differences could be detected between the transplant groups. Flow-cytometric analysis of cell suspensions from spleen and transplants revealed a reduction of T-cells (OX-19+), MHC-I and transferrin-receptor-bearing cells in both transplant groups, and a decrease in the number of Thelper-cells and ED-3+ macrophages in subcutaneous transplants. Both transplant groups were defective regarding the allogeneic and pokeweed mitogen response. Aberration of the lipopolysaccharide response was restricted to subcutaneous transplants, which additionally showed abnormal expression of interferon-gamma, interleukin-5 and interleukin-6 mRNA. Thus, subtle alterations of the newly developed microenvironment and/or lymphocyte-homing may influence the regeneration of splenic tissue; the implantation site may represent an important parameter in functional reorganisation.

Splenic autotransplantation and the immune system. Adequate testing required for evaluation of effect

The risk of severe infections after splenectomy, even after many years, is now well established. In attempts to prevent these infections, spleen-saving techniques, including autotransplantation of spleen fragments, have been performed, when possible in combination with vaccination. The problem in autotransplantation is the evaluation of functional activity. The results of the tests used until now often do not seem to correlate very well with the risk of developing an overwhelming postsplenectomy infection (OPSI). This may be related to the fact that the tests used evaluate general functions, and not specific spleen-related functions, such as the capacity to mount a primary response to certain polysaccharide antigens present in the capsule of bacteria known to cause OPSI. In this review, the significance of the spleen in the human immune system is discussed and the effects of splenectomy are described, including the precautions that can be taken to diminish the risk of postsplenectomy infections and sepsis. It appears that postsplenectomy vaccination is more successful when recently developed protein-conjugated polysaccharide vaccines are used. Because the present testing of the function of spleen autotransplants is not adequate, we suggest that new tests should be developed, employing appropriate polysaccharide antigens.

Regeneration of the spleen and splenic autotransplantation

This paper reviews the subject of regeneration of the spleen and discusses the role of splenic autotransplantation following splenectomy for trauma.

Pneumococcal vaccine improves pulmonary clearance of live pneumococci after splenectomy

The efficacy of pneumococcal capsular polysaccharide vaccines after splenectomy to decrease the incidence of postsplenectomy pneumococcal sepsis is controversial. We examined the effect of pneumococcal vaccine on clearance of live pneumococci from lungs of splenectomized and sham-operated mice following an aerosol challenge of pneumococci. Splenectomy impaired clearance of pneumococci from mouse lungs and allowed for increased translocation of pneumococci to tracheobronchial lymph nodes compared to shams (P less than 0.01). Pneumococcal vaccine improved lung clearance in both splenectomized and sham-operated mice compared to saline controls (P less than 0.01), but the number of live pneumococci recovered from lung pairs was greater in splenectomized mice compared to shams (P less than 0.01). Pneumococcal vaccination facilitated earlier translocation of pneumococci to tracheobronchial lymph nodes, and probably promoted bactericidal activity in these nodes, in both splenectomized and sham-operated mice. Survival in splenectomized mice was improved by vaccination, but remained significantly less than that in saline-treated sham-operated mice (P less than 0.0009). The data show that pneumococcal vaccine can improve lung antipneumococcal defenses in splenectomized mice, but not to the same degree as in mice retaining their spleens. Pneumococcal vaccine should be given after splenectomy, but surgeons should caution patients that it may be less effective than when given to individuals with intact spleens or before elective surgery.

Splenic autotransplantation: determination of the optimum amount required for maximum survival

Splenic salvage in cases of traumatic or iatrogenic injuries may require autotransplantation of splenic fragments when splenorrhaphy or partial splenectomy is not possible. There are no studies which address the issue concerning the optimal amount of spleen to be transplanted in order to yield maximal survival in a model of pneumococcal sepsis. This study uses a Sprague-Dawley rat model to attempt to clarify this issue. Animals were divided into seven groups: control, total splenectomy, 25, 40, 60, 80, and 100% omental pouch autotransplantation. These animals were challenged with intravenous Streptococcus pneumonia Type I after 24 weeks, and mortality and blood culture results were monitored. Transplants were recovered and weights were compared with the weights originally transplanted. Survival and blood culture results were seen to improve in a linear quantitative fashion as the amount of spleen autotransplanted increased up to 80%, after which no further improvement was seen. This data supports the autotransplantation of 80% of the spleen in the Sprague-Dawley rat as the optimum amount to achieve maximal survival in a model of pneumococcal sepsis.

Immunization with heat-killed pneumococci, but not pneumococcal capsular polysaccharides, improves survival in splenectomized mice

Immunization with pneumococcal capsular polysaccharides (pn PS) is advocated after splenectomy to decrease the risk of overwhelming sepsis. The clinical and experimental evidence for the benefit of immunization after splenectomy is controversial. Various reports in the literature have claimed a benefit of immunization after splenectomy, but careful review of methodologies reveals that heat-killed pneumococci (pn) were used to immunize the experimental animals. Since we have not been able to protect splenectomized (splx) mice by immunization with pn PS, we compared survival after live pneumococcal aerosol challenge and antibody (Ab) responses in splx and sham splx mice immunized with either pn PS or heat-killed pn. Immunization with either heat-killed type 3 pn or pn type 3 PS improved survival in sham-splx mice compared to saline controls (p less than 0.001). Only immunization with heat-killed type 3 pn improved survival in splx mice (p less than 0.001), while pn PS had no effect on survival compared to saline splx controls. Ab responses to pn type 3 PS measured by enzyme linked immunosorbent assay were depressed in splx mice compared to sham-splx mice regardless of the method of immunization. Sham-splx mice immunized with heat-killed pn had higher Ab levels compared to mice vaccinated with pn PS (p less than 0.001) suggesting an adjuvant effect in sham-splx mice. The data suggest that immunization with pn PS may not be beneficial to a splx host. Improved survival after immunization with heat-killed bacteria in splx mice may be related to Ab responses to antigens other than the capsular polysaccharide.

Risk of splenic salvage after trauma. Analysis of 200 adults

This review was undertaken to analyze critically the complications resulting from operative splenic salvage. Over a 6 year period, 200 adults who sustained splenic trauma underwent laparotomy. The mechanism of injury was blunt in 138 patients (69 percent), a stab wound in 32 patients (16 percent), and a gunshot wound in 30 patients (15 percent). Splenorrhaphy was accomplished in 85 patients (42 percent). Methods of repair included cautery and hemostatic agents in 24 patients (28 percent), debridement and suturing in 42 patients (50 percent), and partial resection in 19 patients (22 percent). Six patients died, four from head trauma and two from multiple organ failure. Postoperative complications occurred in 14 patients. Four were intraabdominal. Three patients required reoperation for splenic hemorrhage; one (2 percent) after suture repair and two (11 percent) after partial resection. A left subphrenic abscess developed in another patient. Splenic reimplantation was performed in 43 patients (22 percent). Five deaths occurred. One was due to head trauma, three to multiple organ failure, and one to overwhelming pneumococcal infection. Eleven postoperative complications occurred, but none was related to splenic autotransplantation. Despite the enthusiasm for splenic salvage, the number of patients suitable for splenorrhaphy plateaued at 56 percent. Complications of splenorrhaphy are infrequent, and the risk increases with more complex salvage attempts. We believe that splenic reimplantation remains a safe procedure.

Demonstration of functioning heterotopic splenic autografts by scintigraphy

The use of heterotopic splenic autografts is demonstrated as a means of preserving functioning splenic tissue in 15 patients undergoing splenectomy for trauma. In all patients, functioning splenic autografts could be shown by scintigraphy, using 99mTc-labelled erythrocytes or 99mTc-labelled sulphur colloid, performed 12 weeks after implantation.

Penicillin and natural immunity protect against postsplenectomy sepsis

Prophylactic penicillin, splenic autotransplantation, and immunization using pneumococcal vaccine have all been shown to reduce the incidence and mortality of postsplenectomy sepsis. However, little is known regarding the effect of penicillin in established infection or the effect of prior infection in either asplenic controls or animals with autotransplanted splenic tissue. An animal model with bacterial introduction via the lungs was used to investigate the effect of penicillin, splenic autotransplantation, and previous exposure to the infecting organism on the mortality of postsplenectomy sepsis. One hundred fifty-nine rats underwent either sham celiotomy, intraperitoneal splenic autotransplantation, or splenectomy. Twelve weeks postoperatively all animals were challenged using Streptococcus pneumoniae delivered transtracheally. Half of each group received procaine penicillin by intramuscular injection for 5 days beginning 24 hr post bacterial inoculation and mortality was observed. Eight weeks later surviving rats that had received penicillin were reinoculated with the same organism and mortality was again observed. Splenic autotransplantation reduced the early mortality in postsplenectomy sepsis. Prior bacterial exposure reduced the mortality in postsplenectomy sepsis, even in splenectomized animals. Treatment with penicillin produced a marked reduction in mortality even when administration was postponed for 24 hr after bacterial inoculation.

Posttraumatic splenic replantation in children

Previous work in our laboratories showed that canine omental replantation of splenic wafers leads to reproducible viability, restoration of filtrative function, bacterial clearance, and normal antibody formation. An identical technique has been employed in children whose spleen could not be repaired since 1979. During a 3-yr follow-up viability of the replanted segments was documented with return of filtrative function, normal immunoglobulin, and antibody response. Splenic preservation through operative repair or selective nonoperative observation should remain the primary goal after splenic trauma. If this is not possible, splenic replantation represents an alternative approach in the treatment of splenic trauma.

Alternatives to splenectomy in adults after trauma. Repair, partial resection, and reimplantation of splenic tissue

Splenectomy results in a lifelong risk of overwhelming infection in the adult as well as the child. This has prompted our current enthusiasm for splenic salvage in trauma patients. A number of alternatives to total splenectomy exist; however, the complications that result from splenic salvage must not exceed the risk incurred by loss of this organ. Splenorraphy can be performed safely in the majority of patients despite associated intraabdominal injuries. When splenectomy is necessary, reimplantation of splenic tissue is feasible. The efficacy of this technique is preventing postsplenectomy sepsis remains to be established.

Malign effects of splenectomy--the place of conservative treatment

In this review article the incidence is discussed of overwhelming post-splenectomy infection (OPSI), which is especially likely to occur in children and when splenectomy is carried out for haematological disorders. Long-term broad spectrum antibiotics or the use of polyvalent pneumococcal vaccine are often advocated as prophylactic measures under these circumstances.

After mild splenic trauma, conservative surgery or partial splenectomy may be indicated in some cases. Where trauma is more severe and the spleen cannot safely be preserved there may be a place for autotransplantation of splenic slices, for example into a pocket of omentum, and there is some experimental support for this technique.

Splenic and hepatic trauma in children

The concepts for proper management of splenic and hepatic injuries have been evolving over the last several years. The recognition that aggressive surgical therapy in some instances was responsible for the number of life-threatening complications led to a reappraisal of the principles of care for these traumatic lesions. The emerging consensus of opinion is that often nonoperative therapy or more "conservative" operations are preferable. The accumulated experience to date supports the view that this more selective therapeutic approach will result in lower morbidity and mortality for children sustaining splenic or hepatic injuries. Fortunately, the recent technologic improvements in the field of radiology have enabled the clinician to diagnose and serially evaluate these major intra-abdominal injuries with a high degree of confidence.