Immunotherapy in Renal Cell Carcinoma

ABSTRACT: Patients with metastatic renal cell carcinoma continue to present a therapeutic challenge. Current therapeutic approaches involve surgery and various types of immunotherapy. The rationale for this latter form of therapy include the observations of spontaneous tumor regression, the presence of a T-cell–mediated immune response, and the tumor responses observed in patients receiving cytokine therapy. Analysis of prognostic factors in these patients demonstrates that clinical responses occur most frequently in individuals with good performance status. The cytokines interleukin-2 (IL-2, aldesleukin [Proleukin], interferon-alfa (Intron A, Roferon-A) , or the combination produce responses in 15% to 20% of patients. Randomized trials suggest that administration of interferon-alfa may result in a modest improvement in median survival. Investigation of the molecular genetics of renal cell carcinoma and the presence of T-lymphocyte immune dysregulation have suggested new therapeutic strategies. Further preclinical and clinical studies investigating inhibitors of angiogenesis or pharmacologic methods to reverse immune dysregulation are ongoing. Therapeutic results in patients with renal cell carcinoma remain limited, and investigational approaches are warranted. [ONCOLOGY 13(6):801-810, 1999]

Introduction

Renal cell carcinoma is an epithelial malignancy that appears to be slowly increasing in incidence. It is estimated that 30,600 new cases of kidney cancer are diagnosed annually in the United States,[1] and 12,000 deaths result from this tumor each year. Since 1935, the rate of increase of renal cell carcinoma has slowed somewhat but approximates 2% per annum.[2]

Histologically, renal cancer encompasses a heterogeneous group of diseases.[3] The most common histologic type is clear cell cancer (Figure 1a), which accounts for approximately 75% of renal carcinomas. Papillary tumors (Figure 1b) occur in only 15% of patients, and other malignancies, such as sarcomatoid, collecting duct, and medullary tumors, develop in fewer than 5%.

Recent molecular genetic studies have identified mutations of the von Hippel Lindau (VHL) gene in patients with clear cell carcinoma.[4] It appears that vascular endothelial growth factor (VEGF) may be under the regulation of the VHL protein product. Mutant forms of this protein, such as are found in clear cell cancer, may be associated with enhanced expression of VEGF.[5] The vascular nature of renal tumors, together with these observations, suggest that methods to inhibit VEGF expression may be of therapeutic interest.

In addition, some renal tumors express c-met.[6] This proto-oncogene codes for a protein that functions as a receptor for hepatocyte growth factor.

These kinds of studies have provided insights into the genetic defects occurring in renal cancer and may lead to new treatment approaches. Current therapeutic approaches in patients with advanced disease continue to involve surgery and various forms of immunotherapy, however.

Prognostic Factors

Figure 2 shows the distribution by stage of patients with newly diagnosed renal cell carcinoma. Close to half of patients (45%) have localized disease at diagnosis. However, approximately 30% of individuals have metastatic disease, and another 25% have locally advanced tumors with lymph node and/or local organ involvement.

In patients with metastatic renal cell carcinoma, 3- to 5-year survival rates are less than 5%.[7] Outcomes differ in subsets of individuals with advanced disease, however. In patients who have synchronous metastatic disease or who develop metastases within 12 months of surgery, the 2-year survival rate approaches 0%.[8] In contrast, patients in whom metastatic disease develops more than 2 years from diagnosis have a 5-year survival rate of over 20%.[8] In addition, various prognostic factors play an important role in determining therapeutic outcomes in patients with metastatic renal cancer. The most important factor identified to date is performance status.[9]

Immunotherapy

Rationale for Use

The possibility that the immune response may control the progression of cancer was suggested over 40 years ago. In patients with renal cancer, three observations have provided a rationale for the use of immunotherapy.

Spontaneous Regression-The first observation, spontaneous regression, was recognized originally in patients in whom synchronous metastatic disease regressed after removal of the primary tumor. Recent reviews suggest that this phenomenon is very uncommon.[10]

In addition, it has been observed that pulmonary metastases may undergo regression in a subset of patients with metastatic renal cancer. In two trials, one conducted by Oliver and colleagues[11] and the second by the Canadian Urologic Group,[12] approximately 5% to 7% of patients had transient partial regressions of pulmonary nodules that were unrelated to therapy.

T-Cell–Mediated Immune Responses-The second observation is the presence of a T-lymphocyte–mediated immune response in patients with renal cancer. Immunohistologic examination of renal tumors demonstrates infiltration by T-lymphocytes (Figure 3), as well as macrophages.[13] In approximately 25% of patients, these tumor-infiltrating lymphocytes are cytolytic and/or produce cytokines in response to autologous tumor in a major histocompatibility complex (MHC)–restricted fashion.[14] Recent studies have attempted to define the antigens recognized by these T-lymphocytes.[15]

Clinical Responses to Biological Agents-The last observation is the occurrence of clinical responses in patients receiving biological agents, such as the cytokines. The cytokines used have included the interleukin and interferon families, as well as the colony-stimulating factors, such as granulocyte-macrophage colony-stimulating factor (GM-CSF, sargramostim- [Leukine, Prokine]), and macrophage colony-stimulating factor (M-CSF).

Interleukin-2

Of the interleukin family, recombinant human interleukin-2 (rHu-IL-2, aldesleukin [Proleukin]) is the predominant agent used in patients with renal cell carcinoma. This protein is a growth factor that enhances the proliferation and function of T-lymphocytes.[16]

In view of the T-lymphocyte population found in renal tumors, this cytokine was studied in kidney cancer patients. A recent review of clinical results in over 1,700 patients (Table 1) suggests that regression rates in individuals receiving rHu-IL-2 are approximately 15% to 16%.[17]

Three schedules have been used: a high-dose intravenous bolus approach, continuous IV infusion, and subcutaneous administration. In patients receiving high-dose intravenous rHu-IL-2, the complete regression rate was approximately 5%, whereas in those given the other regimens, this frequency tended to be somewhat lower (approximately 2% to 3%). In addition, the complete responses in patients receiving high-dose rHu-IL-2 appeared to be durable in many instances. Overall, however, clinical results did not appear to differ significantly with different methods or schedules of administering rHu-IL-2.

Randomized Trial-In order to compare these approaches, randomized clinical trials are necessary, since prognostic factors can significantly influence the outcome in renal cancer patients. A recent National Cancer Institute (NCI) randomized trial compared high-dose, intravenous-bolus rHu-IL-2 (720,000 IU/kg every 8 hours for 15 doses) with a lower-dose bolus (72,000 IU/kg every 8 hours for 15 doses) schedule in over 200 patients.[18] The overall response rates were 19% and 10% in the high- and low-dose groups, respectively, with no differences in median response duration or median survival between the two groups. Currently, the NCI is conducting a second trial to compare high-dose intravenous rHu-IL-2, a low-dose intravenous regimen, and subcutaneous rHu-IL-2.

Interferon-Alfa

A second cytokine that is widely used for the treatment of renal cancer is interferon-alfa (Intron A, Roferon-A). This pleiotropic protein has antiviral, immunomodulatory, and antiproliferative activities.

A recent review of over 1,500 patients (Table 2) suggested that tumor regression occurs in 12% to 15% of patients following administration of interferon alfa.[3] However, response rates may vary somewhat between the interferon preparations,[3] ranging from 12% to 18%. Complete responses occur in 2% to 5% of patients and are generally seen in individuals with pulmonary metastases.

The optimal therapeutic dose of interferon is not well defined, but appears to be between 5 and 10 MU/m² administered as a subcutaneous injection 3 to 5 days weekly.[19]

Randomized Trials-Unlike rHu-IL-2, randomized trials have been conducted in which interferon-alfa has been compared with other approaches. These include comparisons with non-cytokine–containing regimens and/or regimens containing other cytokines.

The studies of greatest interest (Table 3) are those reported in a preliminary fashion by Pyrhönen et al[20] and Ritchie et al.[21] Pyrhönen et al[20] conducted a trial in approximately 160 patients with metastatic disease who received either interferon-alfa and vinblastine or vinblastine alone. This trial detected significant differences in response rates in patients treated with interferon-alfa plus vinblastine compared with vinblastine alone (16.5% vs 2.5%). Median survival durations also differed significantly between the two groups (15.8 vs 8.8 months). These results suggest that interferon as a single agent may enhance survival since the clinical activity of vinblastine is minimal.[22]

Ritchie et al[21] compared renal cancer patients receiving interferon-alfa (10 MU subcutaneously three times weekly) with those receiving methoxyprogesterone (300 mg/d). This study, which involved over 330 patients, was closed early because of differences in median, 1-, and 2-year survival rates. Clinical results in patients treated with interferon-alfa were significantly better than results in patients given methoxyprogesterone. In patients with measurable disease, interferon-alfa produced responses in 13% and methoxyprogesterone in 7%. This study concluded that interferon-alfa significantly enhances survival in patients with metastatic renal cell carcinoma.

A third trial that was somewhat smaller than the latter two studies did not demonstrate a significant improvement in survival but the trends were suggestive.[23] Thus, the findings of these trials suggest that interferon-alfa may enhance survival in patients with metastatic renal cell cancer, although the effect appears to be modest.

Interferon-Gamma

A second interferon subtype is interferon-gamma-1b (Actimmune). This protein, referred to as immune interferon, is produced by T-cells.[24] Phase I and II studies suggested that responses to interferon-gamma occur in over 15% of patients with renal cancer.[3,25,26]

Recently, the Canadian Urologic Group conducted a randomized, double-blind, placebo-controlled trial of this interferon in over 180 patients with metastatic renal cell carcinoma.[12] Interferon-gamma produced a response rate of 4%, and placebo, a rate of 6%. This trial did not confirm the activity of interferon-gamma in patients with metastatic renal cell carcinoma. It also demonstrates the importance of a randomized trial design when assessing the value of any therapy for patients with metastatic renal cell carcinoma.

Interferon-Alfa Plus rHu-IL-2

The single-agent activity of interferon-alfa and rHu-IL-2 noted in patients with metastatic renal cell carcinoma, and preclinical observations[27] indicating that these two cytokines may have synergistic antitumor activity, led to a series of studies examining the combination of these two proteins. A recent review[16] of over 1,400 patients receiving interferon-alfa and rHu-IL-2 (Table 4) suggests that the overall response rate to the combination is 20%, and that approximately 3% to 5% of patients have complete responses. These results do not appear to depend on the schedule of rHu-IL-2, and occur with either subcutaneous, continuous intravenous infusion, or intravenous boluses.

Randomized Trials-The clinical effects of this combination have been examined in randomized trials by two groups of investigators. Negrier et al[28] performed a three-arm study in 425 patients with renal cancer. The treatments included: (1) a continuous IV infusion of rHu-IL-2 (18 MIU/m²/d) alone, (2) the combination of rHu-IL-2 (at the same dose as in the single-agent arm) and interferon-alfa (6 MU three times weekly), and (3) interferon-alfa (18 MU three times weekly) alone.

Response rates with the cytokine combination were significantly higher than with rHu-IL-2 or interferon-alfa alone (18.6% vs 6.5% and 7.5%, respectively), as was event-free survival at 1 year. Toxicity was substantial, however, with high therapy-related mortality in the rHu-IL-2 and rHu-IL-2–interferon-alfa arms. Finally, there were no differences in overall survival among the three treatment arms. However, upon failure of their assigned therapy, patients were permitted to switch to another treatment arm, thus obscuring possible differences.

Recently, Henriksson et al[29] reported a study in which 128 patients with renal cell carcinoma were randomized to receive tamoxifen (Nolvadex) or the combination of subcutaneous rHu-IL-2, natural leukocyte interferon-alfa, and tamoxifen. No significant difference in median survival between the two treatment groups was detected. Response evaluation was not a primary end point of this trial; however, the authors noted five complete responses in the rHu-IL-2–interferon-alfa group and two in the patients receiving tamoxifen. Based on these results, it appears that the combination of rHu-IL-2 and interferon-alfa may increase response rates. However, it is unclear whether this therapy improves overall survival.

Chemoimmunotherapy

Finally, investigators have been intrigued by the potential synergism of biological agents with chemotherapeutic drugs. Specifically, the combination of interferon-alfa and fluorouracil has been widely investigated in other disease states, and recent data suggest that the combination of rHu-IL-2, interferon-alfa, and fluorouracil may enhance response rates in patients with renal cell carcinoma. In a review of 433 patients receiving various schedules of these three agents, an overall response rate of ~ 27%[30] was found. Response rates varied considerably among studies.

Kirchner et al summarized their experience with 246 patients who received these three agents in a phase II trial.[31] The response rate was 33%, with 11% of patients achieving a complete response. Patient response correlated with prognostic factors.

Randomized Trial-Finally, a randomized trial has been published in preliminary form[32] in which 131 patients were randomized to subcutaenous rHu-IL-2 and interferon-alfa, or the combination of rHu-IL-2, interferon-alfa, and fluorouracil. Low response rates (< 10%) were observed in both arms, with no enhancement by fluorouracil.

Available data suggest that there may be a slight increase in response rates when fluorouracil is administered with rHu-IL-2 and interferon-alfa. However, current results are conflicting, and additional randomized trials of chemoimmunotherapy are necessary.

Current Treatment Approaches

The optimal therapy for patients with metastatic renal cell carcinoma depends on their disease and performance status. For individuals with a solitary metastatic site or surgically approachable disease, resection of metastatic disease is reasonable. Also, individuals with two to four pulmonary metastases may benefit from this approach.[33]

Among patients with unresectable metastatic disease, the groups who stand to benefit most from cytokine therapy are those who are asymptomatic and those who have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. Alternative approaches for these individuals include observation until disease progresses, or use of a cytokine, such as rHu-IL-2, interferon-alfa, or the two agents in combination.

In patients who are symptomatic (ECOG performance status of 3), symptomatic care may be most appropriate. For a more complete discussion of clinical approaches to these patients, readers are referred to a recent review.[3]

Novel Treatment Approaches

In view of the limited efficacy of currently available therapy for metastatic renal cell carcinoma, investigation of novel approaches is of paramount importance. Recent studies have focused on continued exploration of adoptive immune approaches, the use of post-surgical adjuvant therapy, and the role of immunosuppression.

Adoptive Therapy

Adoptive therapy has been extensively investigated in renal cell carcinoma in the past using lymphokine-activated killer cells[34] and tumor-infiltrating lymphocytes.[35,36] These studies suggested that selected patients responded to the adoptive transfer of cells. However, the role of the lymphocyte effectors in these studies was unclear, since concomitant IL-2 was also administered in most trials.

Recent approaches have involved the use of autologous vaccines to generate sensitized T-cells in vivo.[37] Preliminary results suggest that patients may demonstrate tumor regression after receiving only sensitized T-cells. However, the exact nature of the effector cell required and the overall value of this approach remain investigational.

The role of dendritic cells, which present antigen to T-lymphocytes, is also being studied. Dendritic cells include various populations of adherent mononuclear cells that occur in low frequency in peripheral blood.[38] These mononuclear cells can be expanded with cytokine combinations, such as interleukin-4, GM-CSF, and/or tumor necrosis factor.[39] The use of tumor antigens and/or tumor lysates plus dendritic cells as an approach to immunize patients is now under investigation.[39]

Post-Surgical Adjuvant Therapy

Post-surgical adjuvant therapy for patients at high risk of relapse is an approach that has been utilized with some success in other human tumors. A recent study suggested that, following surgery, patients with renal cancer are primarily at risk for systemic relapse.[40] Local relapse can occur but is uncommon overall. Adjuvant approaches to patients with high-risk renal cancer have involved radiation therapy, administration of cytokines, or the use of autologous vaccines.

Several randomized trials of radiotherapy have been reported, including pre-[41,42] and postoperative[43] studies. In each case, no improvement in overall or disease-free survival was seen in irradiated patients.

The adjuvant use of cytokines, such as interferon-alfa or rHu-IL-2, is also under investigation. Several trials using interferon-alfa[44,45] have been conducted in patients with T3 or T4 tumors, as well as those with lymph node-positive disease. Preliminary reports from two of the studies do not suggest any benefit of this approach in terms of disease-free interval or survival. The use of postoperative rHu-IL-2 is now under investigation. Two approaches, one using high-dose bolus rHu-IL-2 and a second using low-dose outpatient subcutaneous rHu-IL-2,[46] are being studied.

Finally, the use of autologous whole cell vaccines has been investigated in renal cancer patients. A randomized trial reported by Galligioni et al[47] did not demonstrate a decrease in recurrence rates among vaccinated patients.

The evidence to date, therefore, indicates that routine postoperative therapy is of no value in high-risk patients. Studies investigating rHu-IL-2, chemoimmunotherapy, and new vaccine strategies are planned.

Role of Immunosuppression

It has been recognized for over 30 years that patients with metastatic malignancies have abnormal immune responses. Recently, multiple abnormalities have been noted in T-lymphocytes obtained from patients with metastatic renal cancer. These include signaling defects,[48] increased levels of apoptosis,[49] and defective T-cell–receptor complexes.[50] The relationship of these abnormalities to tumor status remains unclear, but their presence may be relevant in patients with a malignancy for which immunotherapy plays a prominent therapeutic role.

Initial studies focused on the T-cell–receptor complex.[50] It was observed that the T-cell–receptor epsilon chain was expressed normally, whereas the zeta chain was absent or decreased in patients with metastatic disease. Attempts to relate these findings to outcome and/or prognosis have been unsuccessful.[51]

Recently, abnormalities in the NFkB system have been recognized.[48] This transcription factor regulates genes that are important for T-cell function and growth[52] and prevention of apoptosis.[53] The NFkB family consists of multiple proteins, and, ordinarily, NFkB is sequestered in an inactive form in the cytoplasm by IkBa. Phosphorylation and degradation of IkBa release NFkB, with subsequent translocation and regulation of gene transcription in the nucleus.[52] Abnormalities of NFkB activation (Figure 4) have been recognized in T-cells obtained from patients with renal cell carcinoma.

Preliminary results in 77 patients with varying stages of renal cancer suggest that patients with either localized or metastatic renal cell carcinoma have a much higher frequency of impaired NFkB activation than do patients who are surgically free of disease or individuals who do not have cancer.[54] In 18 patients who were studied prior to and after surgery, T-lymphocytes from 7 patients again demonstrated normal NFkB activation patterns in the postoperative period.

The etiology of this impaired NFkB action remains unclear. Soluble products from tumor explants have been found that suppress T-cell proliferation, NFkB activation, and production of TH1-type cytokines, such as interferon-gamma.[55]

Finally, T-cells that reside within tumors appear to have a higher-than-expected frequency of apoptosis.[Uzzo et al, unpublished data] In addition, when these T-cells are activated with mitogens, apoptosis is enhanced in a subset of individuals. It appears that immune dysregulation is present in over 60% of patients with renal cancer. The exact relationship of immune dysregulation to therapeutic outcome and prognosis remains unclear. It is possible that this abnormality may contribute to the low response rates to immunotherapy involving cytokines.

Conclusions

Metastatic renal cell carcinoma remains a therapeutic challenge. Various immunotherapeutic approaches to renal cell carcinoma result in tumor regression in a small subset of patients who have good performance status. When tested in randomized trials, interferon-alfa appears to improve overall survival to a limited extent.

A clinical schema for approaching patients with metastatic renal cell carcinoma is illustrated in Figure 5. Patients with solitary metastatic sites are candidates for surgery. Individuals with adequate performance status are candidates for cytokine therapy or investigational approaches. The role of chemoimmunotherapy remains to be defined.

Recent studies demonstrating immune dysregulation, suggest that it may decrease the effects of various immunotherapeutic approaches in renal cancer patients. However, additional studies are required to further investigate these abnormalities. Studies of new therapeutic avenues, such as inhibition of angiogenesis and pharmacologic and/or clinical methods to reverse immune dysregulation, are in progress.

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