Melanoma is one of the deadliest malignancies with a high risk of relapse and metastasis. Long-term, tumor-specific, and systemic immunity induced by local intervention is ideal for personalized cancer therapy. Laser immunotherapy (LIT), a combination of local irradiation of laser and local administration of an immunostimulant, was developed to achieve such an immunity. Although LIT showed promising efficacy on tumors, its immunological mechanism is still not understood, especially its spatio-temporal dynamics.

Methods: In this study, we investigated LIT-induced immunological responses using a 980-nm laser and a novel immunostimulant, N-dihydrogalactochitosan (GC). Then we followed the functions of key immune cells spatially and temporally using intravital imaging and immunological assays.

Results: Immediately after LIT, GC induced a rapid infiltration of neutrophils which ingested most GC in tumors. The cytokines released to the serum peaked at 12 h after LIT. Laser irradiations produced photothermal effects to ablate the tumor, release damage-associated molecular patterns, and generate whole-cell tumor vaccines. LIT-treated tumor-bearing mice efficiently resisted the rechallenged tumor and prevented lung metastasis. Intravital imaging of tumor at rechallenging sites in LIT-treated mice revealed that the infiltration of tumor-infiltrating lymphocytes (TILs) increased with highly active motility. Half of TILs with arrest and confined movements indicated that they had long-time interactions with tumor cells. Furthermore, LIT has synergistic effect with checkpoint blockade to improve antitumor efficacy.

Conclusion: Our research revealed the important role of LIT-induced neutrophil infiltration on the in situ whole-cell vaccine-elicited antitumor immune response and long-term T cell immune memory.

黑色素瘤是最致命的恶性肿瘤之一，复发和转移的风险很高。由局部干预引起的长期，肿瘤特异性和全身免疫是个性化癌症治疗的理想选择。激光免疫疗法（LIT）是结合激光局部照射和免疫刺激剂局部给药而开发的，旨在实现这种免疫力。尽管LIT对肿瘤显示出有希望的疗效，但其免疫机制仍不清楚，尤其是其时空动态。

方法：在这项研究中，我们研究了使用980 nm激光和新型免疫刺激剂N-二氢半乳糖苷（GC）对LIT诱导的免疫反应。然后，我们使用活体成像和免疫学方法在空间和时间上跟踪关键免疫细胞的功能。

结果：LIT后，GC立即诱导嗜中性粒细胞快速浸润，并吞噬了肿瘤中的大部分GC。LIT后12小时，释放至血清的细胞因子达到峰值。激光照射产生光热效应，以消融肿瘤，释放与损伤相关的分子模式，并产生全细胞肿瘤疫苗。LIT治疗的荷瘤小鼠有效抵抗了再发肿瘤并预防了肺转移。在LIT处理的小鼠中，在具有挑战性的部位进行的肿瘤活体成像显示，肿瘤浸润淋巴细胞（TILs）的浸润随着高度活跃的运动而增加。一半的TIL具有停滞和局限性运动，表明它们与肿瘤细胞有长期的相互作用。此外，LIT与检查点封锁具有协同作用，可提高抗肿瘤功效。

结论：我们的研究揭示了LIT诱导的中性粒细胞浸润对原位全细胞疫苗引发的抗肿瘤免疫反应和长期T细胞免疫记忆的重要作用。