More than three decades after the discovery of the human immunodeficiency virus (HIV), HIV infections and their consequences remain a major global health concern. Modern antiretroviral therapy (ART) durably suppresses viral replication, improves immune function, and halts clinical disease progression, yet the prevalence of neurological disorders remains persistently high in HIV
+ individuals [
1]. These variegated neurological complications are grouped under the term HIV-associated neurocognitive disorders (HAND). Clinical features of HAND include cognitive deficits in attention, memory, executive function, and informational processing and also particularly cerebellum-associated motor symptoms including gait disturbance, limb weakness, and tremor [
2‐
4]. Infected individuals also frequently exhibit severe affective disturbances early in the course of disease [
5,
6]. The nosology for HAND delineates three levels of severity: HIV-associated asymptomatic neurocognitive impairment (ANI), HIV-associated mild neurocognitive disorders (MND), and HIV-associated dementia (HAD) [
7]. While the most severe manifestation of HAND (HAD) is rare in the era of ART, the prevalence of cognitive deficits overall remains high, even among aviremic patients [
1,
8,
9]. ANI and MND significantly interfere with activities of daily life (e. g., employment, medication management, etc.) and are associated with an increased risk for early development of symptomatic HAND and even increased mortality compared with neuropsychologically unimpaired HIV
+ individuals [
10‐
13]. According to widely recognized theories, neuronal damage is mainly caused by the virus-dependent activation of macrophages and microglia. This alters the production of chemokines and cytokines and leads to a dysregulation of immune functions and production of neurotoxic substances and harmful viral proteins in the brain [
14‐
18]. Previous neuropathological studies of HIV infection focused mainly on neocortical brain areas traditionally associated with higher cognitive functions, including frontal, prefrontal, parietal, and temporal cortices and basal ganglia [
19‐
22]. However, there is also emerging evidence for a role of the cerebellum in higher cognitive functions and more recently for an involvement in HAND [
23]. In fact, the observation that the cerebellar dentate nucleus is expanded in anthropoid apes and humans in parallel with the prefrontal cortex relative to other species has laid foundations for subsequent investigations revealing an emerging role of the cerebellum in many non-motor as well as motor functions [
24]. Thus, a multitude of functional imaging and anatomical and clinical studies support the participation of the cerebellum in cognitive functions such as language, visual-spatial, executive, and working-memory processes [
25‐
28]. Schmahmann and Sherman have promulgated a distinct term for disturbances related to cerebellar damage — the cerebellar cognitive affective syndrome (CCAS) [
29]. Comparing the symptoms of CCAS and HAND, there is striking congruency. Unexplained cerebellar atrophy has been found with neuroimaging in HIV patients indicating that neurodegeneration in the cerebellum occurs as a consequence of HIV infection [
30]. However, it is unexplored which type of cerebellar neurons degenerate and to what extent neuronal cerebellar degeneration is related to neuroinflammatory events within the cerebellum [
31].
Considering this background, the present study systematically investigates for the first time the molecular and cellular patterns of the cerebellar response to lentiviral infection, and the consequences of antiretroviral treatment, in a primate model of HIV infection, the simian immunodeficiency virus (SIV)-infected rhesus macaque.